Bug 1373814 - Add new probe to measure start-up input latency. data-r=francois r=francois,smaug

For parent process, users may expect the UI is interactable after they saw the
first tab has restored/shown.
So this patch added a new topic "sessionstore-one-or-no-tab-restored" which
represents the parent process has finished a tab restoring. If there is nothing
to restore, it is effectively equal to "sessionstore-windows-restored".

For centent processes, users may expect web content is interactable when the
top-level-content-document has finished loading, which is different from the
parent case.

MozReview-Commit-ID: AtEUW80Ea6n

--HG--
extra : rebase_source : d920975bf95545ea9e3127d3f570b814fe301be9

browser/components/sessionstore/SessionStore.jsm

@@ -971,6 +971,8 @@ var SessionStoreInternal = {
         SessionStoreInternal.restoreNextTab();
 
         this._sendTabRestoredNotification(tab, data.isRemotenessUpdate);
+
+        Services.obs.notifyObservers(null, "sessionstore-one-or-no-tab-restored");
         break;
       case "SessionStore:crashedTabRevived":
         // The browser was revived by navigating to a different page
@@ -1149,6 +1151,7 @@ var SessionStoreInternal = {
 
           // Nothing to restore now, notify observers things are complete.
           Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED);
+          Services.obs.notifyObservers(null, "sessionstore-one-or-no-tab-restored");
           this._deferredAllWindowsRestored.resolve();
         } else {
           TelemetryTimestamps.add("sessionRestoreRestoring");
@@ -1168,6 +1171,7 @@ var SessionStoreInternal = {
       } else {
         // Nothing to restore, notify observers things are complete.
         Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED);
+        Services.obs.notifyObservers(null, "sessionstore-one-or-no-tab-restored");
         this._deferredAllWindowsRestored.resolve();
       }
     // this window was opened by _openWindowWithState

layout/base/PresShell.cpp

@@ -560,6 +560,8 @@ mozilla::LazyLogModule PresShell::gLog("PresShell");
 mozilla::TimeStamp PresShell::sLastInputCreated;
 mozilla::TimeStamp PresShell::sLastInputProcessed;
 
+bool PresShell::sProcessInteractable = false;
+
 #ifdef DEBUG
 static void
 VerifyStyleTree(nsPresContext* aPresContext, nsFrameManager* aFrameManager)
@@ -1017,6 +1019,9 @@ PresShell::Init(nsIDocument* aDocument,
 #endif
       os->AddObserver(this, "memory-pressure", false);
       os->AddObserver(this, NS_WIDGET_WAKE_OBSERVER_TOPIC, false);
+      if (XRE_IsParentProcess() && !sProcessInteractable) {
+        os->AddObserver(this, "sessionstore-one-or-no-tab-restored", false);
+      }
     }
   }
 
@@ -1245,6 +1250,9 @@ PresShell::Destroy()
 #endif
       os->RemoveObserver(this, "memory-pressure");
       os->RemoveObserver(this, NS_WIDGET_WAKE_OBSERVER_TOPIC);
+      if (XRE_IsParentProcess()) {
+        os->RemoveObserver(this, "sessionstore-one-or-no-tab-restored");
+      }
     }
   }
 
@@ -8281,6 +8289,32 @@ PresShell::HandleEventInternal(WidgetEvent* aEvent,
         double lastMillis = (sLastInputProcessed - sLastInputCreated).ToMilliseconds();
         Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_COALESCED_MS,
                               lastMillis);
+
+        if (MOZ_UNLIKELY(!sProcessInteractable)) {
+          // For content process, we use the ready state of
+          // top-level-content-document to know if the process has finished the
+          // start-up.
+          // For parent process, see the topic
+          // 'sessionstore-one-or-no-tab-restored' in PresShell::Observe.
+          if (XRE_IsContentProcess() &&
+              mDocument && mDocument->IsTopLevelContentDocument()) {
+            switch (mDocument->GetReadyStateEnum()) {
+              case nsIDocument::READYSTATE_INTERACTIVE:
+              case nsIDocument::READYSTATE_COMPLETE:
+                sProcessInteractable = true;
+                break;
+              default:
+                break;
+            }
+          }
+        }
+        if (MOZ_LIKELY(sProcessInteractable)) {
+          Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_POST_STARTUP_MS,
+                                lastMillis);
+        } else {
+          Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_STARTUP_MS,
+                                lastMillis);
+        }
       }
       sLastInputCreated = aEvent->mTimeStamp;
     } else if (aEvent->mTimeStamp < sLastInputCreated) {
@@ -9719,6 +9753,19 @@ PresShell::Observe(nsISupports* aSubject,
     return NS_OK;
   }
 
+  // For parent process, user may expect the UI is interactable after a
+  // tab (previously opened page or home page) has restored.
+  if (!nsCRT::strcmp(aTopic, "sessionstore-one-or-no-tab-restored")) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    sProcessInteractable = true;
+
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (os) {
+      os->RemoveObserver(this, "sessionstore-one-or-no-tab-restored");
+    }
+    return NS_OK;
+  }
+
   NS_WARNING("unrecognized topic in PresShell::Observe");
   return NS_ERROR_FAILURE;
 }

layout/base/PresShell.h

@@ -902,6 +902,8 @@ protected:
 
   static mozilla::TimeStamp sLastInputCreated;
   static mozilla::TimeStamp sLastInputProcessed;
+
+  static bool               sProcessInteractable;
 };
 
 } // namespace mozilla

toolkit/components/telemetry/Histograms.json

@@ -6520,6 +6520,28 @@
     "releaseChannelCollection": "opt-out",
     "description": "Time (ms) from the Input event being created to the end of it being handled, but with overlapping events coalesced."
   },
+  "INPUT_EVENT_RESPONSE_STARTUP_MS": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["wpan@mozilla.com"],
+    "bug_numbers": [1373814],
+    "expires_in_version": "61",
+    "kind": "exponential",
+    "high": 10000,
+    "n_buckets": 50,
+    "releaseChannelCollection": "opt-out",
+    "description": "Time (ms) from the Input event being created to the end of it being handled, but with overlapping events coalesced, which happens before the process is ready for interaction."
+  },
+  "INPUT_EVENT_RESPONSE_POST_STARTUP_MS": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["wpan@mozilla.com"],
+    "bug_numbers": [1373814],
+    "expires_in_version": "61",
+    "kind": "exponential",
+    "high": 10000,
+    "n_buckets": 50,
+    "releaseChannelCollection": "opt-out",
+    "description": "Time (ms) from the Input event being created to the end of it being handled, but with overlapping events coalesced, which happens after the process is ready for interaction."
+  },
   "LOAD_INPUT_EVENT_RESPONSE_MS": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["perf-telemetry-alerts@mozilla.com"],