Bug 1228147: part 2: Add telemetry probe for synchronous scroll. r=kats

layout/base/nsRefreshDriver.cpp

@@ -441,8 +441,11 @@ private:
     #ifndef ANDROID  /* bug 1142079 */
       if (XRE_IsParentProcess()) {
         TimeDuration vsyncLatency = TimeStamp::Now() - aVsyncTimestamp;
+        uint32_t sample = (uint32_t)vsyncLatency.ToMilliseconds();
         Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_CHROME_FRAME_DELAY_MS,
-                              vsyncLatency.ToMilliseconds());
+                              sample);
+        Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS,
+                              sample);
       } else if (mVsyncRate != TimeDuration::Forever()) {
         TimeDuration contentDelay = (TimeStamp::Now() - mLastChildTick) - mVsyncRate;
         if (contentDelay.ToMilliseconds() < 0 ){
@@ -450,8 +453,11 @@ private:
           // the reported hardware rate. In those cases, consider that we have 0 delay.
           contentDelay = TimeDuration::FromMilliseconds(0);
         }
+        uint32_t sample = (uint32_t)contentDelay.ToMilliseconds();
         Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_CONTENT_FRAME_DELAY_MS,
-                              contentDelay.ToMilliseconds());
+                              sample);
+        Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS,
+                              sample);
       } else {
         // Request the vsync rate from the parent process. Might be a few vsyncs
         // until the parent responds.

layout/generic/nsGfxScrollFrame.cpp

@@ -41,6 +41,7 @@
 #include "mozilla/dom/Element.h"
 #include <stdint.h>
 #include "mozilla/MathAlgorithms.h"
+#include "mozilla/Telemetry.h"
 #include "FrameLayerBuilder.h"
 #include "nsSMILKeySpline.h"
 #include "nsSubDocumentFrame.h"
@@ -1510,6 +1511,8 @@ public:
     , mCallee(nullptr)
     , mOneDevicePixelInAppUnits(aPresContext->DevPixelsToAppUnits(1))
   {
+    Telemetry::SetHistogramRecordingEnabled(
+      Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, true);
   }
 
   NS_INLINE_DECL_REFCOUNTING(AsyncSmoothMSDScroll, override)
@@ -1598,6 +1601,8 @@ private:
   // Private destructor, to discourage deletion outside of Release():
   ~AsyncSmoothMSDScroll() {
     RemoveObserver();
+    Telemetry::SetHistogramRecordingEnabled(
+      Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, false);
   }
 
   nsRefreshDriver* RefreshDriver(ScrollFrameHelper* aCallee) {
@@ -1634,12 +1639,17 @@ public:
   explicit AsyncScroll(nsPoint aStartPos)
     : AsyncScrollBase(aStartPos)
     , mCallee(nullptr)
-  {}
+  {
+    Telemetry::SetHistogramRecordingEnabled(
+      Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, true);
+  }
 
 private:
   // Private destructor, to discourage deletion outside of Release():
   ~AsyncScroll() {
     RemoveObserver();
+    Telemetry::SetHistogramRecordingEnabled(
+      Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, false);
   }
 
 public:

toolkit/components/telemetry/Histograms.json

@@ -4135,6 +4135,15 @@
     "bug_numbers": [1221674],
     "description": "Delay in ms between the target and the actual handling time of the frame at refresh driver in the content process."
   },
+  "FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS": {
+    "alert_emails": ["perf-telemetry-alerts@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "exponential",
+    "high": "10000",
+    "n_buckets": 50,
+    "bug_numbers": [1228147],
+    "description": "Delay in ms between the target and the actual handling time of the frame at refresh driver while scrolling synchronously."
+  },
   "FX_TAB_SWITCH_UPDATE_MS": {
     "alert_emails": ["perf-telemetry-alerts@mozilla.com"],
     "expires_in_version": "never",

toolkit/components/telemetry/Telemetry.cpp

@@ -909,6 +909,7 @@ IsHistogramEnumId(Telemetry::ID aID)
 
 // List of histogram IDs which should have recording disabled initially.
 const Telemetry::ID kRecordingInitiallyDisabledIDs[] = {
+  Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS,
 
   // The array must not be empty. Leave these item here.
   Telemetry::TELEMETRY_TEST_COUNT_INIT_NO_RECORD,