Record size of scroller that user scrolls

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 6d05fe059f6f8a7ddb8b1370866f43cd5abda5ea..7777ef150b7db56b9da194032a8c5b528748c445 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -22,7 +22,9 @@
 #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 "platform/scroll/ScrollerSize.h"
 #include "wtf/PtrUtil.h"
 
 namespace blink {
@@ -221,6 +223,13 @@ WebInputEventResult ScrollManager::handleGestureScrollBegin(
   passScrollGestureEvent(gestureEvent,
                          m_scrollGestureHandlingNode->layoutObject());
 
+  if (m_scrollGestureHandlingNode->layoutObject() &&
+      (gestureEvent.sourceDevice == WebGestureDeviceTouchpad ||
+       gestureEvent.sourceDevice == WebGestureDeviceTouchscreen)) {
+    recordScrollerSize(*(m_scrollGestureHandlingNode->layoutObject()),
+                       gestureEvent.sourceDevice);
+  }
+
   m_currentScrollChain.clear();
   std::unique_ptr<ScrollStateData> scrollStateData =
       WTF::makeUnique<ScrollStateData>();
@@ -559,4 +568,30 @@ bool ScrollManager::canHandleGestureEvent(
   return false;
 }
 
+void ScrollManager::recordScrollerSize(const LayoutObject& layoutObject,
+                                       const WebGestureDevice device) {
+  if (!layoutObject.enclosingLayer())
+    return;
+
+  if (device == WebGestureDeviceTouchpad) {
+    DEFINE_STATIC_LOCAL(
+        CustomCountHistogram, sizeHistogramWheel,
+        ("Event.Scroll.ScrollerSize.OnScroll_Wheel", 1,
+         LayerTreeHostImpl::m_pairForScrollerSizeHistograms.first,
+         LayerTreeHostImpl::m_pairForScrollerSizeHistograms.second));
+    sizeHistogramWheel.count(
+        layoutObject.enclosingLayer()->visualRect().width().toInt() *
+        layoutObject.enclosingLayer()->visualRect().height().toInt());
+  } else {
+    DEFINE_STATIC_LOCAL(
+        CustomCountHistogram, sizeHistogramTouch,
+        ("Event.Scroll.ScrollerSize.OnScroll_Touch", 1,
+         LayerTreeHostImpl::m_pairForScrollerSizeHistograms.first,
+         LayerTreeHostImpl::m_pairForScrollerSizeHistograms.second));
+    sizeHistogramTouch.count(
+        layoutObject.enclosingLayer()->visualRect().width().toInt() *
+        layoutObject.enclosingLayer()->visualRect().height().toInt());
+  }
+}
+
 }  // namespace blink