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

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..6a4268196170aaf2f42111d8618fad97dd1d37d8 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;

[bokan, 2017/03/28 15:30:15]

This should be false. It's used in Android WebView to send scrolls directly to
the viewport layers, skipping hit tests.

+    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, NonCompositedMainThreadScrollingReasonTest) {
+  setHtmlInnerHTML(
+      "<style>.box { width: 100px; height: 100px; overflow: scroll; }"
+      ".translucent { opacity: 0.5; will-change:transform;} .spacer { height: "
+      "1000px;} body {height: 1000px; }"
+      ".border { border: 5px solid; border-radius: 2px; } </style>"
+      "<div class='translucent box'><div class='spacer'></div></div>"
+      "<div class='border box'><div class='spacer'></div></div>");

[bokan, 2017/03/28 15:30:15]

Please add at least one case that checks that a composited (and maybe main
thread scrolled) box doesn't add to the counts.

I'd also add a case where you have a composited scroller over a non-composited
scroller. I believe that should cause the scroll events to go to the main thread
even if scrolling over the composited box.

+
+  HistogramTester histogramTester;
+  // Test wheel scroll
+  ScrollBeginEventBuilder wheelScrollBegin(
+      IntPoint(50, 50), FloatPoint(0.f, 1.f), WebGestureDeviceTouchpad);
+  document().frame()->eventHandler().handleGestureEvent(wheelScrollBegin);
+  histogramTester.expectBucketCount("Renderer4.MainThreadWheelScrollReason", 17,
+                                    1);
+
+  wheelScrollBegin.y = wheelScrollBegin.globalY = 150;
+  document().frame()->eventHandler().handleGestureEvent(wheelScrollBegin);

[bokan, 2017/03/28 15:30:15]

You should send a ScrollEnd after each scrollBegin, just to make sure we don't
confuse the EventHandler.

+  histogramTester.expectBucketCount("Renderer4.MainThreadWheelScrollReason", 20,
+                                    1);
+  // Test touch scroll
+  ScrollBeginEventBuilder touchScrollBegin(
+      IntPoint(50, 50), FloatPoint(0.f, 1.f), WebGestureDeviceTouchscreen);
+  document().frame()->eventHandler().handleGestureEvent(touchScrollBegin);
+  histogramTester.expectBucketCount("Renderer4.MainThreadGestureScrollReason",
+                                    17, 1);
+
+  document().frame()->eventHandler().handleGestureEvent(touchScrollBegin);
+  histogramTester.expectBucketCount("Renderer4.MainThreadGestureScrollReason",
+                                    17, 2);
+}
+
 class TooltipCapturingChromeClient : public EmptyChromeClient {
  public:
   TooltipCapturingChromeClient() {}