Record size of scroller that user scrolls

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

Index: third_party/WebKit/Source/core/input/EventHandlerTest.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandlerTest.cpp b/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
index f8618151f6be13253f4f4efeefa617b8fe13d3b2..f8ff35244fff6b57bdbd4ea6f68a931e7beee7f7 100644
--- a/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
@@ -16,6 +16,7 @@
 #include "core/page/AutoscrollController.h"
 #include "core/page/Page.h"
 #include "core/testing/DummyPageHolder.h"
+#include "platform/testing/HistogramTester.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
@@ -79,6 +80,22 @@ class MousePressEventBuilder : public WebMouseEvent {
   }
 };
 
+class ScrollBeginEventBuilder : public WebGestureEvent {
+ public:
+  ScrollBeginEventBuilder(IntPoint position,
+                          FloatPoint delta,
+                          WebGestureDevice device)
+      : WebGestureEvent() {
+    m_type = WebInputEvent::GestureScrollBegin;
+    x = globalX = position.x();
+    y = globalY = position.y();
+    data.scrollBegin.deltaYHint = delta.y();
+    data.scrollBegin.targetViewport = true;
+    sourceDevice = device;
+    m_frameScale = 1;
+  }
+};
+
 void EventHandlerTest::SetUp() {
   m_dummyPageHolder = DummyPageHolder::create(IntSize(300, 400));
 }
@@ -461,6 +478,39 @@ TEST_F(EventHandlerTest, dragEndInNewDrag) {
   // This test passes if it doesn't crash.
 }
 
+TEST_F(EventHandlerTest,
+       ScrollerSizeOfMainThreadScrollingHistogramRecordingTest) {
+  setHtmlInnerHTML(
+      "<style>"
+      " .box {width: 100px; height: 100px; overflow: scroll; opacity: 0.5; }"
+      " .spacer { height: 1000px;} body {height: 1000px; }"
+      "</style>"
+      "<div class='box'>"
+      " <div id='content' class='spacer'></div>"
+      "</div>");
+
+  HistogramTester histogramTester;
+
+  // Test wheel scroll on the box

[tdresser, 2017/03/30 14:41:35]

Missing .

+  ScrollBeginEventBuilder wheelScrollBegin(
+      IntPoint(50, 50), FloatPoint(0.f, 1.f), WebGestureDeviceTouchpad);
+
+  document().frame()->eventHandler().handleGestureEvent(wheelScrollBegin);
+  histogramTester.expectTotalCount("Event.Scroll.ScrollerSize.OnScroll_Wheel",
+                                   1);
+  histogramTester.expectBucketCount("Event.Scroll.ScrollerSize.OnScroll_Wheel",
+                                    10000, 1);
+
+  // Test touch scroll on the main frame

[tdresser, 2017/03/30 14:41:35]

Missing .

+  ScrollBeginEventBuilder touchScrollBegin(
+      IntPoint(200, 200), FloatPoint(0.f, 1.f), WebGestureDeviceTouchscreen);
+  document().frame()->eventHandler().handleGestureEvent(touchScrollBegin);
+  histogramTester.expectTotalCount("Event.Scroll.ScrollerSize.OnScroll_Touch",
+                                   1);
+  histogramTester.expectBucketCount("Event.Scroll.ScrollerSize.OnScroll_Touch",
+                                    200000, 1);
+}
+
 class TooltipCapturingChromeClient : public EmptyChromeClient {
  public:
   TooltipCapturingChromeClient() {}