Record non-stacking-context as main thread scrolling reasons

third_party/WebKit/Source/web/tests/ScrollMetricsTest.cpp

 // Copyright 2017 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 "core/dom/ClientRect.h"
 #include "core/frame/FrameView.h"
 #include "core/input/EventHandler.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/scroll/MainThreadScrollingReason.h"
@@ skipping 329 matching lines @@
 
   Element* box = GetDocument().getElementById("inner");
   HistogramTester histogram_tester;
 
   Scroll(box, kWebGestureDeviceTouchpad);
   // Scrolling the inner box will gather reasons from the scrolling chain. The
   // inner box itself has no reason because it's composited. Other scrollable
   // areas from the chain have corresponding reasons.
   EXPECT_WHEEL_BUCKET(kHasOpacityAndLCDText, 1);
   EXPECT_WHEEL_BUCKET(kBackgroundNotOpaqueInRectAndLCDText, 1);
+  EXPECT_WHEEL_BUCKET(kIsNotStackingContextAndLCDText, 1);
   EXPECT_WHEEL_BUCKET(kHasBorderRadius, 1);
   EXPECT_WHEEL_BUCKET(kHasTransformAndLCDText, 0);
-  EXPECT_WHEEL_TOTAL(3);
+  EXPECT_WHEEL_TOTAL(4);
 }
 
 }  // namespace
 
 }  // namespace blink