Fix the position of the gray vertical line for line length limit

A special treatment for commit messages was added in Change I18048f53f,
but the limit was not updated when the file path changed.

Bug: Issue 10626
Change-Id: I6db1e539ce2f66d0b0a38d3524fb5ff0afe75b98
(cherry picked from commit cd79eaca3a)

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js

@@ -83,7 +83,10 @@
       },
       /** @type {?} */
       patchRange: Object,
-      path: String,
+      path: {
+        type: String,
+        observer: '_pathObserver',
+      },
       prefs: {
         type: Object,
         observer: '_prefsObserver',
@@ -586,6 +589,11 @@
       }
     },
 
+    _pathObserver() {
+      // Call _prefsChanged(), because line-limit style value depends on path.
+      this._prefsChanged(this.prefs);
+    },
+
     _viewModeObserver() {
       this._prefsChanged(this.prefs);
     },