Add Interaction.CHANGE_ID_CHANGED reporting event

Unfortunately the NAVIGATION event is fired too early and does not
include the `changeId`, but it is also very tricky to move it, so
instead fire another event that can act as the start of a changeId
based user journey.

Release-Notes: skip
Change-Id: I2635d66b3ddd0bd1f7f5e7f9147b2c6625484f33

polygerrit-ui/app/constants/reporting.ts

diff --git a/polygerrit-ui/app/constants/reporting.ts b/polygerrit-ui/app/constants/reporting.ts
index 109ec9b..dded0c6 100644
--- a/polygerrit-ui/app/constants/reporting.ts
+++ b/polygerrit-ui/app/constants/reporting.ts
@@ -152,4 +152,7 @@
   FILE_LIST_DIFF_EXPANDED = 'file-list-diff-expanded',
   FILE_LIST_ALL_DIFFS_COLLAPSED = 'file-list-all-diffs-collapsed',
   FILE_LIST_ALL_DIFFS_EXPANDED = 'file-list-all-diffs-expanded',
+  // The very first reporting event with `ChangeId` set when visiting a change
+  // related page. Can be used as a starting point for user journeys.
+  CHANGE_ID_CHANGED = 'change-id-changed',
 }

polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts

diff --git a/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts b/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
index 84b9481..08c9e36 100644
--- a/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
+++ b/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
@@ -612,8 +612,9 @@
     this.time(Timing.DIFF_VIEW_CONTENT_DISPLAYED);
     this.time(Timing.DIFF_VIEW_DISPLAYED);
     this.time(Timing.FILE_LIST_DISPLAYED);
-    this.reportRepoName = undefined;
-    this.reportChangeId = undefined;
+
+    this.setRepoName(undefined);
+    this.setChangeId(undefined);
     // reset slow rpc list since here start page loads which report these rpcs
     this.slowRpcList = [];
     this.hiddenDurationTimer.reset();
@@ -998,12 +999,17 @@
     );
   }
 
-  setRepoName(repoName: string) {
+  setRepoName(repoName?: string) {
     this.reportRepoName = repoName;
   }
 
-  setChangeId(changeId: NumericChangeId) {
+  setChangeId(changeId?: NumericChangeId) {
+    const originalChangeId = this.reportChangeId;
     this.reportChangeId = changeId;
+
+    if (!!changeId && changeId !== originalChangeId) {
+      this.reportInteraction(Interaction.CHANGE_ID_CHANGED, {changeId});
+    }
   }
 }