Cancel diff processing when the diff processor is detached

Bug: Issue 4730
Change-Id: I50cae3c2c59b447befdccde3fcb4bf4a7dadcae8

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

@@ -86,6 +86,7 @@
     },
 
     detached: function() {
+      this.cancel();
       this.unlisten(window, 'scroll', '_handleWindowScroll');
     },
 

polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.html

@@ -591,5 +591,12 @@ limitations under the License.
         });
       });
     });
+
+    test('detaching cancels', function() {
+      element = fixture('basic');
+      sandbox.stub(element, 'cancel');
+      element.detached();
+      assert(element.cancel.called);
+    });
   });
 </script>