Bug 1100920 - telemetry probe for frames latency. r=roc

layout/base/nsRefreshDriver.cpp

@@ -51,6 +51,8 @@
 #include "nsDocShell.h"
 #include "nsISimpleEnumerator.h"
 
+#include "mozilla/Telemetry.h"
+
 using namespace mozilla;
 using namespace mozilla::widget;
 
@@ -296,6 +298,7 @@ protected:
         this,
         (aNowTime - mTargetTime).ToMilliseconds(),
         delay);
+    Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_FRAME_DELAY_MS, (aNowTime - mTargetTime).ToMilliseconds());
 
     // then schedule the timer
     LOG("[%p] scheduling callback for %d ms (2)", this, delay);
@@ -410,6 +413,7 @@ protected:
         this,
         (aNowTime - mTargetTime).ToMilliseconds(),
         delay);
+    Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_FRAME_DELAY_MS, (aNowTime - mTargetTime).ToMilliseconds());
 
     // then schedule the timer
     LOG("[%p] scheduling callback for %d ms (2)", this, delay);

toolkit/components/telemetry/Histograms.json

@@ -3512,6 +3512,13 @@
     "n_buckets": 30,
     "description": "Average paint duration during any tab open/close animation (excluding tabstrip scroll)"
   },
+  "FX_REFRESH_DRIVER_FRAME_DELAY_MS": {
+    "expires_in_version": "default",
+    "kind": "exponential",
+    "high": "10000",
+    "n_buckets": 50,
+    "description": "Delay in ms between the target and the actual handling time of the frame at refresh driver"
+  },
   "FX_TAB_SWITCH_UPDATE_MS": {
     "alert_emails": ["perf-telemetry-alerts@mozilla.com"],
     "expires_in_version": "40",