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

third_party/WebKit/Source/core/input/ScrollManager.cpp

Index: third_party/WebKit/Source/core/input/ScrollManager.cpp
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.cpp b/third_party/WebKit/Source/core/input/ScrollManager.cpp
index 727c3e74e57525196f5f4abb1ec12c18a21ecc4c..b50e85310355506bba5da51275e924cc7bac6e77 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -22,6 +22,7 @@
 #include "core/page/scrolling/RootScrollerController.h"
 #include "core/page/scrolling/ScrollState.h"
 #include "core/paint/PaintLayer.h"
+#include "platform/Histogram.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "wtf/PtrUtil.h"
 
@@ -196,6 +197,67 @@ void ScrollManager::customizedScroll(const Node& startNode,
   scrollState.distributeToScrollChainDescendant();
 }
 
+uint32_t ScrollManager::computeNonCompositedMainThreadScrollingReasons() {
+  // When scrolling on the main thread, the scrollableArea may or may not be
+  // composited. Either way, we have recorded either the reasons that

[bokan, 2017/04/06 21:45:09]

nit: "reasons that stored" -> "reasons stored"

[yigu, 2017/04/07 16:35:32]

Done.

+  // stored in its layer or the reason NonFastScrollableRegion from the
+  // compositor side. Here we record scrolls that occurred on main thread
+  // due to a non-composited scroller.
+  if (!m_scrollGestureHandlingNode->layoutObject() || !m_frame->view())
+    return 0;
+
+  uint32_t nonCompositedMainThreadScrollingReasons = 0;
+
+  for (auto* curBox =
+           m_scrollGestureHandlingNode->layoutObject()->enclosingBox();
+       curBox; curBox = curBox->containingBlock()) {
+    PaintLayerScrollableArea* scrollableArea = curBox->getScrollableArea();
+
+    if (!scrollableArea || !scrollableArea->scrollsOverflow())
+      continue;
+
+    DCHECK(!scrollableArea->usesCompositedScrolling() ||
+           !nonCompositedMainThreadScrollingReasons);
+    nonCompositedMainThreadScrollingReasons =

[bokan, 2017/04/06 21:45:09]

this should be |=, right?

[yigu, 2017/04/07 16:35:32]

Done.

+        scrollableArea->getNonCompositedMainThreadScrollingReasons();
+  }
+
+  return nonCompositedMainThreadScrollingReasons;
+}
+
+void ScrollManager::recordNonCompositedMainThreadScrollingReasons(
+    const WebGestureDevice device) {
+  if (device != WebGestureDeviceTouchpad &&
+      device != WebGestureDeviceTouchscreen) {
+    return;
+  }
+
+  uint32_t reasons = computeNonCompositedMainThreadScrollingReasons();
+  if (!reasons)
+    return;
+  DCHECK(MainThreadScrollingReason::NonCompositedScrollReasons(reasons));

[bokan, 2017/04/06 21:45:09]

It wouldn't hurt to DCHECK that we don't have any mainThread or CompositorSet
reasons.

[yigu, 2017/04/07 16:35:32]

Current DCHECK guarantees that the reason doesn't include MainThreadCanSet or
CompositedCanSet reasons.

[bokan, 2017/04/07 17:39:03]

Ah, my bad, I didn't pay close enough attention to how these methods work. Now
that I take a look though I think we should change it to my understanding (which
is what the other call site uses). See my comment in the function definition. It
means you'll have to also DCHECK here that we don't have any of the other types
here.

+
+  uint32_t mainThreadScrollingReasonEnumMax =

[bokan, 2017/04/06 21:45:10]

unused

[yigu, 2017/04/07 16:35:32]

It's used in DEFINE_STATIC_LOCAL.

[bokan, 2017/04/07 17:39:03]

Doh

+      MainThreadScrollingReason::kMainThreadScrollingReasonCount + 1;
+  for (uint32_t i = MainThreadScrollingReason::kNonCompositedReasonsFirst;
+       i <= MainThreadScrollingReason::kNonCompositedReasonsLast; ++i) {
+    unsigned val = 1 << i;
+    if (reasons & val) {
+      if (device == WebGestureDeviceTouchscreen) {
+        DEFINE_STATIC_LOCAL(EnumerationHistogram, touchHistogram,
+                            ("Renderer4.MainThreadGestureScrollReason",
+                             mainThreadScrollingReasonEnumMax));
+        touchHistogram.count(i + 1);
+      } else {
+        DEFINE_STATIC_LOCAL(EnumerationHistogram, wheelHistogram,
+                            ("Renderer4.MainThreadWheelScrollReason",
+                             mainThreadScrollingReasonEnumMax));
+        wheelHistogram.count(i + 1);
+      }
+    }
+  }
+}
+
 WebInputEventResult ScrollManager::handleGestureScrollBegin(
     const WebGestureEvent& gestureEvent) {
   Document* document = m_frame->document();
@@ -221,6 +283,8 @@ WebInputEventResult ScrollManager::handleGestureScrollBegin(
   passScrollGestureEvent(gestureEvent,
                          m_scrollGestureHandlingNode->layoutObject());
 
+  recordNonCompositedMainThreadScrollingReasons(gestureEvent.sourceDevice);
+
   m_currentScrollChain.clear();
   std::unique_ptr<ScrollStateData> scrollStateData =
       WTF::makeUnique<ScrollStateData>();