Bug 1892660 - Add a metric for async stylesheet load time. r=jesup

Differential Revision: https://phabricator.services.mozilla.com/D208660

layout/base/metrics.yaml

@@ -29,6 +29,22 @@ performance.pageload:
       - perf-telemetry-alerts@mozilla.com
     expires: never
 
+  async_sheet_load:
+    type: timing_distribution
+    time_unit: millisecond
+    description: >
+      Time spent in milliseconds since a style sheet started loading async
+      until it finished.
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1892660
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1892660
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - emilio@mozilla.com
+      - perf-telemetry-alerts@mozilla.com
+    expires: 132
 
 performance.responsiveness:
   req_anim_frame_callback:

layout/style/Loader.cpp

@@ -18,12 +18,11 @@
 #include "mozilla/AutoRestore.h"
 #include "mozilla/LoadInfo.h"
 #include "mozilla/Logging.h"
+#include "mozilla/glean/GleanMetrics.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/PreloadHashKey.h"
 #include "mozilla/ResultExtensions.h"
-#include "mozilla/SchedulerGroup.h"
 #include "mozilla/URLPreloader.h"
-#include "nsIChildChannel.h"
 #include "nsIPrincipal.h"
 #include "nsISupportsPriority.h"
 #include "nsITimedChannel.h"
@@ -47,8 +46,6 @@
 #include "nsMimeTypes.h"
 #include "nsICSSLoaderObserver.h"
 #include "nsThreadUtils.h"
-#include "nsGkAtoms.h"
-#include "nsIThreadInternal.h"
 #include "nsINetworkPredictor.h"
 #include "nsQueryActor.h"
 #include "nsStringStream.h"
@@ -62,13 +59,10 @@
 #include "mozilla/StyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
 #include "mozilla/ConsoleReportCollector.h"
-#include "mozilla/ServoUtils.h"
 #include "mozilla/css/StreamLoader.h"
 #include "mozilla/SharedStyleSheetCache.h"
 #include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/StaticPrefs_network.h"
-#include "mozilla/StaticPrefs_dom.h"
-#include "mozilla/StaticPrefs_network.h"
 #include "mozilla/Try.h"
 #include "ReferrerInfo.h"
 
@@ -417,6 +411,23 @@ SheetLoadData::~SheetLoadData() {
                      "dropping the load");
 }
 
+void SheetLoadData::StartLoading() {
+  MOZ_ASSERT(!mIsLoading, "Already loading? How?");
+  mIsLoading = true;
+  mLoadStart = TimeStamp::Now();
+}
+
+void SheetLoadData::SetLoadCompleted() {
+  MOZ_ASSERT(mIsLoading, "Not loading?");
+  MOZ_ASSERT(!mLoadStart.IsNull());
+  mIsLoading = false;
+  // Belts and suspenders just in case.
+  if (MOZ_LIKELY(!mLoadStart.IsNull())) {
+    glean::performance_pageload::async_sheet_load.AccumulateRawDuration(
+        TimeStamp::Now() - mLoadStart);
+  }
+}
+
 RefPtr<StyleSheet> SheetLoadData::ValueForCache() const {
   // We need to clone the sheet on insertion to the cache because otherwise the
   // stylesheets can keep full windows alive via either their JS wrapper, or via

layout/style/SheetLoadData.h

@@ -239,6 +239,9 @@ class SheetLoadData final
   // listening for the load.
   bool mIntentionallyDropped = false;
 
+  // The start timestamp for the load.
+  TimeStamp mLoadStart;
+
   const bool mRecordErrors;
 
   bool ShouldDefer() const { return mWasAlternate || !mMediaMatched; }
@@ -269,8 +272,9 @@ class SheetLoadData final
   bool IsLoading() const override { return mIsLoading; }
   bool IsCancelled() const override { return mIsCancelled; }
 
-  void StartLoading() override { mIsLoading = true; }
-  void SetLoadCompleted() override { mIsLoading = false; }
+  void StartLoading() override;
+  void SetLoadCompleted() override;
+
   void Cancel() override { mIsCancelled = true; }
 
  private: