Move logic of recording main thread scrolling reasons from cc to blink::ScrollManager

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 20b84d1c4936211dbfaafe0c9ffb4c2fbecbbdee..7666da4f622996ade3652dccaaa86282838beb39 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -556,6 +556,8 @@ void InputHandlerProxy::RecordMainThreadScrollingReasons(
   // greater than the sample value. kMainThreadScrollingReasonCount doesn't
   // include the NotScrollingOnMain enum but the histograms do so adding
   // the +1 is necessary.
+  // Here we only record NotScrollingOnMain. The actual main thread scrolling
+  // reasons are recorded in blink::ScrollManager.
   uint32_t mainThreadScrollingReasonEnumMax =
       cc::MainThreadScrollingReason::kMainThreadScrollingReasonCount + 1;
   if (reasons == cc::MainThreadScrollingReason::kNotScrollingOnMain) {
@@ -571,29 +573,6 @@ void InputHandlerProxy::RecordMainThreadScrollingReasons(
           mainThreadScrollingReasonEnumMax);
     }
   }
-
-  for (uint32_t i = 0;

[bokan, 2017/03/24 17:55:55]

Sorry, on second thought, we shouldn't remove this. The reasons you've added are
really "NonCompositedScrollerReasons". This records other reasons we might
scroll on the main thread (all the reasons captured in
MainThreadCanSetScrollReasons()) for scrollers that are still composited. And
there's also compositor set reasons (CompositorCanSetScrollReasons()) that the
main-thread doesn't know about.

All the "style-related" reasons you've added you should split out of
MainThreadCanSetScrollReasons() into a separate method called
NonCompositedScrollReasons(). DCHECK that we're never recording one here.
They're not really MainThreadCanSetScrollReasons since we never set them on a
ScrollNode/cc::Layer.

[yigu, 2017/03/27 21:02:08]

Done.

-       i < cc::MainThreadScrollingReason::kMainThreadScrollingReasonCount;
-       ++i) {
-    unsigned val = 1 << i;
-    if (reasons & val) {
-      if (val == cc::MainThreadScrollingReason::kHandlingScrollFromMainThread) {
-        // We only want to record "Handling scroll from main thread" reason if
-        // it's the only reason. If it's not the only reason, the "real" reason
-        // for scrolling on main is something else, and we only want to pay
-        // attention to that reason.
-        if (reasons & ~val)
-          continue;
-      }
-      if (device == blink::WebGestureDeviceTouchscreen) {
-        UMA_HISTOGRAM_ENUMERATION(kGestureHistogramName, i + 1,
-                                  mainThreadScrollingReasonEnumMax);
-      } else {
-        UMA_HISTOGRAM_ENUMERATION(kWheelHistogramName, i + 1,
-                                  mainThreadScrollingReasonEnumMax);
-      }
-    }
-  }
 }
 
 void InputHandlerProxy::RecordScrollingThreadStatus(