diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
index 5f1fd90178..bf787088a3 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
@@ -142,10 +142,7 @@ limitations under the License.
         },
 
         getContentByLine: function(lineNumber, opt_side, opt_root) {
-          var root = Polymer.dom(opt_root || this.diffElement);
-          var sideSelector = !!opt_side ? ('.' + opt_side) : '';
-          return root.querySelector('td.lineNum[data-value="' + lineNumber +
-              '"]' + sideSelector + ' ~ td.content .contentText');
+          return this._builder.getContentByLine(lineNumber, opt_side, opt_root);
         },
 
         getContentByLineEl: function(lineEl) {
@@ -162,19 +159,10 @@ limitations under the License.
         },
 
         getContentsByLineRange: function(startLine, endLine, opt_side) {
-          var groups =
-              this._builder.getGroupsByLineRange(startLine, endLine, opt_side);
-          // In each group, search Element for lines in range.
-          return groups.reduce((function(acc, group) {
-            for (var line = startLine; line <= endLine; line++) {
-              var content =
-                  this.getContentByLine(line, opt_side, group.element);
-              if (content) {
-                acc.push(content);
-              }
-            }
-            return acc;
-          }).bind(this), []);
+          var result = [];
+          this._builder.findLinesByRange(startLine, endLine, opt_side, null,
+              result);
+          return result;
         },
 
         getCommentThreadByLine: function(lineNumber, opt_side, opt_root) {
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.js b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.js
index 79188373f9..fb2d230a6e 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.js
@@ -109,6 +109,66 @@
     return groups;
   };
 
+  GrDiffBuilder.prototype.getContentByLine = function(lineNumber, opt_side,
+      opt_root) {
+    var root = Polymer.dom(opt_root || this._outputEl);
+    var sideSelector = !!opt_side ? ('.' + opt_side) : '';
+    return root.querySelector('td.lineNum[data-value="' + lineNumber +
+        '"]' + sideSelector + ' ~ td.content .contentText');
+  };
+
+  /**
+   * Find line elements or line objects by a range of line numbers and a side.
+   *
+   * @param {Number} start The first line number
+   * @param {Number} end The last line number
+   * @param {String} opt_side The side of the range. Either 'left' or 'right'.
+   * @param {Array<GrDiffLine>} out_lines The output list of line objects. Use
+   *     null if not desired.
+   * @param  {Array<HTMLElement>} out_elements The output list of line elements.
+   *     Use null if not desired.
+   */
+  GrDiffBuilder.prototype.findLinesByRange = function(start, end, opt_side,
+      out_lines, out_elements) {
+    var groups = this.getGroupsByLineRange(start, end, opt_side);
+
+    groups.forEach(function(group) {
+      group.lines.forEach(function(line) {
+        if ((opt_side === 'left' && line.type === GrDiffLine.Type.ADD) ||
+            (opt_side === 'right' && line.type === GrDiffLine.Type.REMOVE)) {
+          return;
+        }
+        var lineNumber = opt_side === 'left' ?
+            line.beforeNumber : line.afterNumber;
+        if (lineNumber < start || lineNumber > end) { return; }
+
+        if (out_lines) { out_lines.push(line); }
+        if (out_elements) {
+          var content = this.getContentByLine(lineNumber, opt_side,
+              group.element);
+          if (content) { out_elements.push(content); }
+        }
+      }.bind(this));
+    }.bind(this));
+  };
+
+  /**
+   * Re-renders the DIV.contentText alement for the given side and range of diff
+   * content.
+   */
+  GrDiffBuilder.prototype._renderContentByRange = function(start, end, side) {
+    var lines = [];
+    var elements = [];
+    var line;
+    var el;
+    this.findLinesByRange(start, end, side, lines, elements);
+    for (var i = 0; i < lines.length; i++) {
+      line = lines[i];
+      el = elements[i];
+      el.parentElement.replaceChild(this._createTextEl(line).firstChild, el);
+    }
+  };
+
   GrDiffBuilder.prototype.getSectionsByLineRange = function(
       startLine, endLine, opt_side) {
     return this.getGroupsByLineRange(startLine, endLine, opt_side).map(
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder_test.html b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder_test.html
index 727ae9bc89..12c8f3c5ca 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder_test.html
@@ -23,7 +23,9 @@ limitations under the License.
 <script src="../gr-diff/gr-diff-line.js"></script>
 <script src="../gr-diff/gr-diff-group.js"></script>
 <script src="gr-diff-builder.js"></script>
+<script src="../../../scripts/util.js"></script>
 
+<link rel="import" href="../gr-diff-cursor/mock-diff-response_test.html">
 <link rel="import" href="gr-diff-builder.html">
 
 <test-fixture id="basic">
@@ -40,6 +42,14 @@ limitations under the License.
   </template>
 </test-fixture>
 
+<test-fixture id="mock-diff">
+  <template>
+    <gr-diff-builder view-mode="SIDE_BY_SIDE">
+      <table id="diffTable"></table>
+    </gr-diff-builder>
+  </template>
+</test-fixture>
+
 <script>
   suite('gr-diff-builder tests', function() {
     var element;
@@ -476,5 +486,83 @@ limitations under the License.
         assert.strictEqual(sections[1], section[1]);
       });
     });
+
+    suite('mock-diff', function() {
+      var element;
+      var builder;
+      var diff;
+
+      setup(function(done) {
+        element = fixture('mock-diff');
+        diff = document.createElement('mock-diff-response').diffResponse;
+
+        var prefs = {
+          line_length: 80,
+          show_tabs: true,
+          tab_size: 4,
+        };
+
+        function doneHandler() {
+          element.removeEventListener('render', doneHandler);
+          builder = element._builder;
+          done();
+        }
+        element.addEventListener('render', doneHandler);
+
+        element.render(diff, {left: [], right: []}, prefs);
+      });
+
+      test('getContentByLine', function() {
+        var actual;
+
+        actual = builder.getContentByLine(2, 'left');
+        assert.equal(actual.textContent, diff.content[0].ab[1]);
+
+        actual = builder.getContentByLine(2, 'right');
+        assert.equal(actual.textContent, diff.content[0].ab[1]);
+
+        actual = builder.getContentByLine(5, 'left');
+        assert.equal(actual.textContent, diff.content[2].ab[0]);
+
+        actual = builder.getContentByLine(5, 'right');
+        assert.equal(actual.textContent, diff.content[1].b[0]);
+      });
+
+      test('findLinesByRange', function() {
+        var lines = [];
+        var elems = [];
+        var start = 6;
+        var end = 10;
+        var count = end - start + 1;
+
+        builder.findLinesByRange(start, end, 'right', lines, elems);
+
+        assert.equal(lines.length, count);
+        assert.equal(elems.length, count);
+
+        for (var i = 0; i < 5; i++) {
+          assert.instanceOf(lines[i], GrDiffLine);
+          assert.equal(lines[i].afterNumber, start + i);
+          assert.instanceOf(elems[i], HTMLElement);
+          assert.equal(lines[i].text, elems[i].textContent);
+        }
+      });
+
+      test('_renderContentByRange', function() {
+        var spy = sinon.spy(builder, '_createTextEl');
+        var start = 9;
+        var end = 14;
+        var count = end - start + 1;
+
+        builder._renderContentByRange(start, end, 'left');
+
+        assert.equal(spy.callCount, count);
+        spy.getCalls().forEach(function(call, i) {
+          assert.equal(call.args[0].beforeNumber, start + i);
+        });
+
+        spy.restore();
+      });
+    });
   });
 </script>