Bug 1385453 - Add Telemetry to measure how successful speculative tab warming is when switching tabs. r=billm,liuche, data-review=liuche

MozReview-Commit-ID: GSMEE3IUlzN

--HG--
extra : rebase_source : be219d2caea47e5050efa3414e941e10bd1ee1e8

browser/base/content/tabbrowser.xml

@@ -4788,6 +4788,23 @@
                 return;
               }
 
+              let warmingState = "disqualified";
+
+              if (this.warmingTabs.has(tab)) {
+                let tabState = this.getTabState(tab);
+                if (tabState == this.STATE_LOADING) {
+                  warmingState = "stillLoading";
+                } else if (tabState == this.STATE_LOADED) {
+                  warmingState = "loaded";
+                }
+              } else if (this.canWarmTab(tab)) {
+                warmingState = "notWarmed";
+              }
+
+              Services.telemetry
+                      .getHistogramById("FX_TAB_SWITCH_REQUEST_TAB_WARMING_STATE")
+                      .add(warmingState);
+
               this.unwarmTab(tab);
 
               this._requestingTab = true;

toolkit/components/telemetry/Histograms.json

@@ -6049,6 +6049,21 @@
     "releaseChannelCollection": "opt-out",
     "description": "Firefox: If the spinner interstitial displays during tab switching, records the time in ms the graphic is visible. This probe is similar to FX_TAB_SWITCH_SPINNER_VISIBLE_MS, but is for truly degenerate cases."
   },
+  "FX_TAB_SWITCH_REQUEST_TAB_WARMING_STATE": {
+    "record_in_processes": ["main"],
+    "expires_in_version": "63",
+    "alert_emails": ["mconley@mozilla.com"],
+    "releaseChannelCollection": "opt-out",
+    "kind": "categorical",
+    "labels": [
+      "disqualified",
+      "notWarmed",
+      "stillLoading",
+      "loaded"
+    ],
+    "bug_numbers": [1385453],
+    "description": "Firefox: When a tab is selected, records whether or not the tab was speculatively 'warmed up' to improve tab switch time."
+  },
   "FX_TAB_CLICK_MS": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "default",