Show helpful instructions if change has Merge conflicts

* If the change has Merge Conflicts, then we show the user some helpful error
message in the tooltip of the change.

Bug: Issue 11501
Change-Id: I14a6b911ecd5a6798adcfe593a9e11a3959e803b
(cherry picked from commit 319ce419fa8f8e0f7574d1febeeb61487fc1ab9a)
diff --git a/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status.js b/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status.js
index 3afbe54..e6f52c6 100644
--- a/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status.js
+++ b/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status.js
@@ -29,6 +29,10 @@
       'It will not appear on dashboards unless you are CC\'ed or assigned, ' +
       'and email notifications will be silenced until the review is started.';
 
+  const MERGE_CONFLICT_TOOLTIP = 'This change has merge conflicts. ' +
+      'Download the patch and run "git rebase master". ' +
+      'Upload a new patchset after resolving all merge conflicts.';
+
   const PRIVATE_TOOLTIP = 'This change is only visible to its owner and ' +
       'current reviewers (or anyone with "View Private Changes" permission).';
 
@@ -75,6 +79,9 @@
         case ChangeStates.PRIVATE:
           this.tooltipText = PRIVATE_TOOLTIP;
           break;
+        case ChangeStates.MERGE_CONFLICT:
+          this.tooltipText = MERGE_CONFLICT_TOOLTIP;
+          break;
         default:
           this.tooltipText = '';
           break;
diff --git a/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status_test.html b/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status_test.html
index 3ac4016..421c6ab5 100644
--- a/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-change-status/gr-change-status_test.html
@@ -35,6 +35,17 @@
 </test-fixture>
 
 <script>
+  const WIP_TOOLTIP = 'This change isn\'t ready to be reviewed or submitted. ' +
+      'It will not appear on dashboards unless you are CC\'ed or assigned, ' +
+      'and email notifications will be silenced until the review is started.';
+
+  const MERGE_CONFLICT_TOOLTIP = 'This change has merge conflicts. ' +
+    'Download the patch and run "git rebase master". ' +
+    'Upload a new patchset after resolving all merge conflicts.';
+
+  const PRIVATE_TOOLTIP = 'This change is only visible to its owner and ' +
+      'current reviewers (or anyone with "View Private Changes" permission).';
+
   suite('gr-change-status tests', () => {
     let element;
     let sandbox;
@@ -51,7 +62,7 @@
     test('WIP', () => {
       element.status = 'WIP';
       assert.equal(element.$$('.chip').innerText, 'Work in Progress');
-      assert.isDefined(element.tooltipText);
+      assert.equal(element.tooltipText, WIP_TOOLTIP);
       assert.isTrue(element.classList.contains('wip'));
     });
 
@@ -81,14 +92,14 @@
     test('merge conflict', () => {
       element.status = 'Merge Conflict';
       assert.equal(element.$$('.chip').innerText, element.status);
-      assert.equal(element.tooltipText, '');
+      assert.equal(element.tooltipText, MERGE_CONFLICT_TOOLTIP);
       assert.isTrue(element.classList.contains('merge-conflict'));
     });
 
     test('private', () => {
       element.status = 'Private';
       assert.equal(element.$$('.chip').innerText, element.status);
-      assert.isDefined(element.tooltipText);
+      assert.equal(element.tooltipText, PRIVATE_TOOLTIP);
       assert.isTrue(element.classList.contains('private'));
     });