Move gr-diff-comment-thread factory to diff-host

This is now only used from there, so it no longer needs to be globally
accessible on Gerrit.

Change-Id: I6facd64ece360f5b8ddf7b801621e86bd5f39697
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.html b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.html
index 028e44c..d335e7a 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.html
@@ -20,7 +20,6 @@
 <link rel="import" href="../../core/gr-reporting/gr-reporting.html">
 <link rel="import" href="../../shared/gr-rest-api-interface/gr-rest-api-interface.html">
 <link rel="import" href="../gr-diff-comment-thread/gr-diff-comment-thread.html">
-<link rel="import" href="../gr-diff-comment-thread-group/gr-diff-comment-thread-group.html">
 <link rel="import" href="../gr-diff/gr-diff.html">
 
 <dom-module id="gr-diff-host">
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.js b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.js
index 2b91060..5e4a3fd 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.js
@@ -599,15 +599,36 @@
     },
 
     _createThreadElement(thread) {
-      const threadEl = Gerrit.createThreadElement(
-          thread, this._parentIndex, this.changeNum, this.path,
-          this.projectName);
+      const threadEl = document.createElement('gr-diff-comment-thread');
       threadEl.className = 'comment-thread';
-      threadEl.addEventListener('thread-discard', e => {
+      threadEl.comments = thread.comments;
+      threadEl.commentSide = thread.commentSide;
+      threadEl.isOnParent = !!thread.isOnParent;
+      threadEl.parentIndex = this._parentIndex;
+      threadEl.changeNum = this.changeNum;
+      threadEl.patchNum = thread.patchNum;
+      threadEl.lineNum = thread.lineNum;
+      const rootIdChangedListener = changeEvent => {
+        thread.rootId = changeEvent.detail.value;
+      };
+      threadEl.addEventListener('root-id-changed', rootIdChangedListener);
+      threadEl.path = this.path;
+      threadEl.projectName = this.projectName;
+      threadEl.range = thread.range;
+      const threadDiscardListener = e => {
+        const threadEl = /** @type {!Node} */ (e.currentTarget);
+
+        const parent = Polymer.dom(threadEl).parentNode;
+        Polymer.dom(parent).removeChild(threadEl);
+
         const i = this._threadEls.findIndex(
             threadEl => threadEl.rootId == e.detail.rootId);
         this._threadEls.splice(i, 1);
-      });
+
+        threadEl.removeEventListener('root-id-changed', rootIdChangedListener);
+        threadEl.removeEventListener('thread-discard', threadDiscardListener);
+      };
+      threadEl.addEventListener('thread-discard', threadDiscardListener);
       return threadEl;
     },
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
index 790a71f..c7ee1c2 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
@@ -55,6 +55,32 @@
       sandbox.restore();
     });
 
+    test('thread-discard handling', () => {
+      const threads = [
+        {comments: [{id: 4711}]},
+        {comments: [{id: 42}]},
+      ];
+      element._parentIndex = 1;
+      element.changeNum = '2';
+      element.path = 'some/path';
+      element.projectName = 'Some project';
+      const threadEls = threads.map(
+          thread => element._createThreadElement(thread));
+      assert.equal(threadEls.length, 2);
+      assert.equal(threadEls[0].rootId, 4711);
+      assert.equal(threadEls[1].rootId, 42);
+      for (const threadEl of threadEls) {
+        Polymer.dom(element).appendChild(threadEl);
+      }
+
+      threadEls[0].dispatchEvent(
+          new CustomEvent('thread-discard', {detail: {rootId: 4711}}));
+      const attachedThreads = element.queryAllEffectiveChildren(
+          'gr-diff-comment-thread');
+      assert.equal(attachedThreads.length, 1);
+      assert.equal(attachedThreads[0].rootId, 42);
+    });
+
     test('reload() cancels before network resolves', () => {
       const cancelStub = sandbox.stub(element.$.diff, 'cancel');