Fix recording of kAnimatingScrollOnMain

ui/events/blink/input_handler_proxy_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/blink/input_handler_proxy.h"
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/test/histogram_tester.h"
@@ skipping 2767 matching lines @@
   input_handler_->RecordMainThreadScrollingReasonsForTest(
       blink::WebGestureDeviceTouchpad,
       cc::MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects |
           cc::MainThreadScrollingReason::kThreadedScrollingDisabled |
           cc::MainThreadScrollingReason::kPageOverlay |
           cc::MainThreadScrollingReason::kAnimatingScrollOnMainThread);
 
   EXPECT_THAT(
       histogram_tester().GetAllSamples("Renderer4.MainThreadWheelScrollReason"),
       testing::ElementsAre(base::Bucket(1, 1), base::Bucket(3, 1),
+                           base::Bucket(5, 1)));
+
+  // We only want to record "animating scroll on 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. So we should only include this reason in the histogram when its on
+  // its own.
+  input_handler_->RecordMainThreadScrollingReasonsForTest(
+      blink::WebGestureDeviceTouchpad,
+      cc::MainThreadScrollingReason::kAnimatingScrollOnMainThread);
+
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("Renderer4.MainThreadWheelScrollReason"),
+      testing::ElementsAre(base::Bucket(1, 1), base::Bucket(3, 1),
                            base::Bucket(5, 1), base::Bucket(14, 1)));
 }
 
 
 INSTANTIATE_TEST_CASE_P(AnimateInput,
                         InputHandlerProxyTest,
                         testing::ValuesIn(test_types));
 }  // namespace test
 }  // namespace ui