Centralized comment requests

Formerly, gr-diff would make its own REST calls for diff comments in the
patch range and path being viewed. However, these calls by the diff view
were redundant to the more general comment requests made by either
gr-diff-view (which requests all comments to support skipping to the
next file with comments) or gr-change-view (which requests comments
individually for each inline diff).

With this change, the diff component no longer loads comments for
itself, but is rather provided the comments from its host view via a
public property. In this way the host view can load the more-general
comment data, and filter it down for the diff view's params.

Introduces the gr-comment-api component to simplify loading and
filtering diff comments for use by diff views. By using this new
component:
* The diff view makes only one request for comments (including drafts
  and robot comments) to support skipping to the next comment and
  displaying comments in the diff view.
* The change view makes only one request for comments for all inline
  diffs.

Bug: Issue 5299
Change-Id: Ia14a01619f1f9881aa0d253fd3f49af9a17f3dce

polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
index afba895..8ff75c1 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
@@ -56,7 +56,7 @@
         getDiffChangeDetail() { return Promise.resolve(null); },
         getChangeFiles() { return Promise.resolve({}); },
         saveFileReviewed() { return Promise.resolve(); },
-        getDiffRobotComments() { return Promise.resolve(); },
+        getDiffRobotComments() { return Promise.resolve({}); },
         getDiffDrafts() { return Promise.resolve(); },
       });
       element = fixture('basic');
@@ -639,57 +639,41 @@
       assert.equal(element._getDiffViewMode(), 'SIDE_BY_SIDE');
     });
 
-    suite('_loadCommentMap', () => {
+    suite('_loadComments', () => {
       test('empty', done => {
-        stub('gr-rest-api-interface', {
-          getDiffComments() { return Promise.resolve({}); },
+        stub('gr-comment-api', {
+          loadAll() { return Promise.resolve(); },
+          getPaths() { return {}; },
+          getCommentsForPath() { return {meta: {}}; },
         });
-        element._loadCommentMap().then(map => {
-          assert.equal(Object.keys(map).length, 0);
+        element._loadComments().then(() => {
+          assert.equal(Object.keys(element._commentMap).length, 0);
           done();
         });
       });
 
-      test('paths in patch range', done => {
-        stub('gr-rest-api-interface', {
-          getDiffComments() {
-            return Promise.resolve({
+      test('has paths', done => {
+        stub('gr-comment-api', {
+          loadAll() { return Promise.resolve(); },
+          getPaths() {
+            return {
               'path/to/file/one.cpp': [{patch_set: 3, message: 'lorem'}],
               'path-to/file/two.py': [{patch_set: 5, message: 'ipsum'}],
-            });
+            };
           },
+          getCommentsForPath() { return {meta: {}}; },
         });
         element._changeNum = '42';
         element._patchRange = {
           basePatchNum: '3',
           patchNum: '5',
         };
-        element._loadCommentMap().then(map => {
-          assert.deepEqual(Object.keys(map),
+        element._loadComments().then(() => {
+          assert.deepEqual(Object.keys(element._commentMap),
               ['path/to/file/one.cpp', 'path-to/file/two.py']);
           done();
         });
       });
-
-      test('empty for paths outside patch range', done => {
-        stub('gr-rest-api-interface', {
-          getDiffComments() {
-            return Promise.resolve({
-              'path/to/file/one.cpp': [{patch_set: PARENT, message: 'lorem'}],
-              'path-to/file/two.py': [{patch_set: 2, message: 'ipsum'}],
-            });
-          },
-        });
-        element._changeNum = '42';
-        element._patchRange = {
-          basePatchNum: '3',
-          patchNum: '5',
-        };
-        element._loadCommentMap().then(map => {
-          assert.equal(Object.keys(map).length, 0);
-          done();
-        });
-      });
     });
 
     suite('_computeCommentSkips', () => {