Reland of place pinch scrollbars with regular scrollbars. (patchset #1 id:1 of...

Reland of place pinch scrollbars with regular scrollbars. (patchset #1 id:1 of https://codereview.chromium.org/1318603005/ )

Reason for revert:
After discussion with samuong@, the original patch should be OK to reland as is and https://codereview.chromium.org/1317153002 is an appropriate fix for the crasher.

Original issue's description:
> Revert of Replace pinch scrollbars with regular scrollbars. (patchset #10 id:180001 of https://codereview.chromium.org/1308053003/ )
> 
> Reason for revert:
> Introduced ChromeDriver devtools mobile emulation crash https://code.google.com/p/chromedriver/issues/detail?id=1205
> 
> Original issue's description:
> > Replace pinch scrollbars with regular scrollbars.
> > 
> > This patch makes the visual-viewport-managed scrollbars exclusive to
> > Android and improves normal scrollbars to be usable during pinch as follows:
> > 
> > 1. Attach the scrollbar layers to the visual viewport, so they're always
> >    onscreen as you zoom in (as already shipped on Mac).
> > 2. Set the container layer to the inner clip layer, so that the size and
> >    position of the thumb reflects the sum of the two viewports,
> >    instead of just the layout viewport.
> > 
> > Note that result of these changes is visually indistiguishable at
> > minimum page scale.  It only improves the behavior when zoomed in.
> > 
> > BUG=523056
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201285
> 
> TBR=rbyers@chromium.org,skobes@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=523056
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201333

TBR=rbyers@chromium.org,skobes@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=523056

Review URL: https://codereview.chromium.org/1305223004

git-svn-id: svn://svn.chromium.org/blink/trunk@201337 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/TestExpectations

@@ -917,6 +917,20 @@ crbug.com/492511 [ Mac ] fast/text/atsui-negative-spacing-features.html [ ImageO
 crbug.com/492511 [ Mac ] fast/text/atsui-spacing-features.html [ ImageOnlyFailure ]
 crbug.com/492511 [ Mac ] fast/text/international/arabic-justify.html [ ImageOnlyFailure ]
 
+crbug.com/523056 compositing/fixed-body-background-positioned.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/vertical-scroll-composited.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/overflow/fixed-position-ancestor-clip.html [ NeedsRebaseline ]
+crbug.com/523056 fast/repaint/absolute-position-changed.html [ NeedsRebaseline ]
+crbug.com/523056 virtual/prefer_compositing_to_lcd_text/compositing/overflow/fixed-position-ancestor-clip.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-composited-page-scale-down.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-iframe-composited-page-scale-down.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-transform-composited-page-scale-down.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-iframe-composited-page-scale.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-composited-page-scale.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/geometry/fixed-position-transform-composited-page-scale.html [ NeedsRebaseline ]
+crbug.com/523056 compositing/scaling/tiled-layer-recursion.html [ NeedsRebaseline ]
+
 # Temporary, until [Unforgeable] attributes have the right accessors 'get' and 'set'.
 crbug.com/491006 http/tests/security/cross-origin-access-over-property-descriptor.html [ Failure ]
 
@@ -1013,8 +1027,6 @@ crbug.com/509025 [ Yosemite ] paint/invalidation/animated-gif.html [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/custom/absolute-sized-content-with-resources.xhtml [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/custom/bug78807.svg [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/text/text-rescale.html [ Failure ]
-crbug.com/509025 [ Yosemite ] compositing/geometry/fixed-position-iframe-composited-page-scale-down.html [ ImageOnlyFailure ]
-crbug.com/509025 [ Yosemite ] compositing/geometry/fixed-position-iframe-composited-page-scale.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/iframes/iframe-copy-on-scroll.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/do-not-paint-outline-into-composited-scrolling-contents.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/update-widget-positions-on-nested-frames-and-scrollers.html [ ImageOnlyFailure Failure Timeout ]
@@ -1061,7 +1073,6 @@ crbug.com/509025 [ Yosemite ] virtual/prefer_compositing_to_lcd_text/scrollbars/
 crbug.com/509025 [ Yosemite ] virtual/threaded/compositing/visibility/visibility-image-layers.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] virtual/threaded/printing/return-from-printing-mode.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] paint/inline/outline-offset.html [ Missing ]
-crbug.com/509025 [ Yosemite ] compositing/geometry/vertical-scroll-composited.html [ Failure ]
 crbug.com/509025 [ Yosemite ] fast/block/lineboxcontain/block-with-ideographs.xhtml [ Failure ]
 # TODO(tkent): Needs to increase padding-right.
 crbug.com/509025 [ Yosemite ] fast/encoding/denormalised-voiced-japanese-chars.html [ Failure ]

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-composited-page-scale-down.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-composited-page-scale.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-iframe-composited-page-scale-down.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-iframe-composited-page-scale.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-transform-composited-page-scale-down.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position-transform-composited-page-scale.html

@@ -2,6 +2,10 @@
 <html>
 <head>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 .fixed-no-z-index {
   position: absolute;
   left: 10px;

third_party/WebKit/LayoutTests/compositing/geometry/fixed-position.html

@@ -7,6 +7,10 @@
   <title>Position fixed</title>
   <script src="../resources/mock_scrollbars.js"></script>
   <style type="text/css" media="screen">
+    ::-webkit-scrollbar {
+      width: 0px;
+      height: 0px;
+    }
     body {
       height: 1000px;
       width: 1000px;

third_party/WebKit/LayoutTests/compositing/geometry/vertical-scroll-composited.html

@@ -5,7 +5,12 @@
     if (window.testRunner)
         testRunner.waitUntilDone();
     </script>
-    <script src="../resources/mock_scrollbars.js"></script>
+    <style>
+    ::-webkit-scrollbar {
+      width: 0px;
+      height: 0px;
+    }
+    </style>
 </head>
 <body style="height: 600px">
 <div style="transform: rotate3d(0,0,1,20deg); width: 800px; height: 1000px; border-style: solid; border-color: Red; border-width: 3px; background-image: url(../resources/apple.jpg); background-repeat:repeat"></div>

third_party/WebKit/LayoutTests/compositing/overflow/fixed-position-ancestor-clip.html

@@ -4,6 +4,10 @@
 <head>
   <title>Position fixed with transform</title>
   <style type="text/css" media="screen">
+    ::-webkit-scrollbar {
+      width: 0px;
+      height: 0px;
+    }
     body {
       height: 1000px;
       width: 1000px;

third_party/WebKit/LayoutTests/compositing/scaling/tiled-layer-recursion.html

@@ -3,6 +3,10 @@
 <html>
 <head>
   <style>
+    ::-webkit-scrollbar {
+      width: 0px;
+      height: 0px;
+    }
     .composited {
       background-color: green;
       width: 200px;

third_party/WebKit/LayoutTests/fast/repaint/absolute-position-changed.html

@@ -2,6 +2,10 @@
 <head>
     <link rel="stylesheet" href="resources/default.css">
     <style>
+        ::-webkit-scrollbar {
+            width: 0px;
+            height: 0px;
+        }
         html {
             overflow: scroll;
         }

third_party/WebKit/LayoutTests/fast/scrolling/overflow-clip-with-page-scale.html

@@ -8,6 +8,10 @@ internals.settings.setViewportMetaEnabled(true);
 </script>
 <script src="../../resources/run-after-layout-and-paint.js"></script>
 <style>
+::-webkit-scrollbar {
+    width: 0px;
+    height: 0px;
+}
 body {
   width: 1000px;
   height: 1000px;

third_party/WebKit/Source/core/frame/FrameView.cpp

@@ -666,6 +666,13 @@ bool FrameView::usesCompositedScrolling() const
     return false;
 }
 
+GraphicsLayer* FrameView::layerForScrollbarContainer() const
+{
+    if (m_frame->isMainFrame())
+        return page()->frameHost().visualViewport().layerForScrollbarContainer();
+    return layerForContainer();
+}
+
 GraphicsLayer* FrameView::layerForScrolling() const
 {
     LayoutView* layoutView = this->layoutView();

third_party/WebKit/Source/core/frame/FrameView.h

@@ -345,6 +345,7 @@ public:
     IntRect scrollableAreaBoundingBox() const override;
     bool scrollAnimatorEnabled() const override;
     bool usesCompositedScrolling() const override;
+    GraphicsLayer* layerForScrollbarContainer() const override;
     GraphicsLayer* layerForScrolling() const override;
     GraphicsLayer* layerForHorizontalScrollbar() const override;
     GraphicsLayer* layerForVerticalScrollbar() const override;

third_party/WebKit/Source/core/frame/VisualViewport.cpp

@@ -49,7 +49,7 @@
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/GraphicsLayerFactory.h"
 #include "platform/scroll/Scrollbar.h"
-#include "platform/scroll/ScrollbarTheme.h"
+#include "platform/scroll/ScrollbarThemeOverlay.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "public/platform/WebLayer.h"
@@ -106,8 +106,7 @@ void VisualViewport::setSize(const IntSize& size)
         m_innerViewportContainerLayer->setSize(m_size);
 
         // Need to re-compute sizes for the overlay scrollbars.
-        setupScrollbar(WebScrollbar::Horizontal);
-        setupScrollbar(WebScrollbar::Vertical);
+        initializeScrollbars();
     }
 
     if (autosizerNeedsUpdating) {
@@ -273,11 +272,9 @@ bool VisualViewport::magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoi
 //  |                   +-- outerViewportContainerLayer (fixed pos container) [frame container layer in DeprecatedPaintLayerCompositor]
 //  |                   |   +-- outerViewportScrollLayer [frame scroll layer in DeprecatedPaintLayerCompositor]
 //  |                   |       +-- content layers ...
-//  |                   +-- horizontal ScrollbarLayer (non-overlay)
-//  |                   +-- verticalScrollbarLayer (non-overlay)
-//  |                   +-- scroll corner (non-overlay)
-//  +- *horizontalScrollbarLayer (overlay)
-//  +- *verticalScrollbarLayer (overlay)
+//  +- horizontalScrollbarLayer
+//  +- verticalScrollbarLayer
+//  +- scroll corner (non-overlay only)
 //
 void VisualViewport::attachToLayerTree(GraphicsLayer* currentLayerTreeRoot, GraphicsLayerFactory* graphicsLayerFactory)
 {
@@ -324,21 +321,33 @@ void VisualViewport::attachToLayerTree(GraphicsLayer* currentLayerTreeRoot, Grap
         m_innerViewportContainerLayer->addChild(m_overscrollElasticityLayer.get());
         m_overscrollElasticityLayer->addChild(m_pageScaleLayer.get());
         m_pageScaleLayer->addChild(m_innerViewportScrollLayer.get());
-        m_innerViewportContainerLayer->addChild(m_overlayScrollbarHorizontal.get());
-        m_innerViewportContainerLayer->addChild(m_overlayScrollbarVertical.get());
 
         // Ensure this class is set as the scroll layer's ScrollableArea.
         coordinator->scrollableAreaScrollLayerDidChange(this);
 
-        // Setup the inner viewport overlay scrollbars.
-        setupScrollbar(WebScrollbar::Horizontal);
-        setupScrollbar(WebScrollbar::Vertical);
+        initializeScrollbars();
     }
 
     m_innerViewportScrollLayer->removeAllChildren();
     m_innerViewportScrollLayer->addChild(currentLayerTreeRoot);
 }
 
+void VisualViewport::initializeScrollbars()
+{
+    if (visualViewportSuppliesScrollbars()) {
+        if (!m_overlayScrollbarHorizontal->parent())
+            m_innerViewportContainerLayer->addChild(m_overlayScrollbarHorizontal.get());
+        if (!m_overlayScrollbarVertical->parent())
+            m_innerViewportContainerLayer->addChild(m_overlayScrollbarVertical.get());
+    } else {
+        m_overlayScrollbarHorizontal->removeFromParent();
+        m_overlayScrollbarVertical->removeFromParent();
+    }
+
+    setupScrollbar(WebScrollbar::Horizontal);
+    setupScrollbar(WebScrollbar::Vertical);
+}
+
 void VisualViewport::setupScrollbar(WebScrollbar::Orientation orientation)
 {
     bool isHorizontal = orientation == WebScrollbar::Horizontal;
@@ -347,17 +356,10 @@ void VisualViewport::setupScrollbar(WebScrollbar::Orientation orientation)
     OwnPtr<WebScrollbarLayer>& webScrollbarLayer = isHorizontal ?
         m_webOverlayScrollbarHorizontal : m_webOverlayScrollbarVertical;
 
-    int thumbThickness = frameHost().settings().pinchOverlayScrollbarThickness();
-    int scrollbarThickness = thumbThickness;
-    int scrollbarMargin = scrollbarThickness;
-
-    // FIXME: Rather than manually creating scrollbar layers, we should create
-    // real scrollbars so we can reuse all the machinery from ScrollbarTheme.
-#if OS(ANDROID)
-    thumbThickness = ScrollbarTheme::theme()->thumbThickness(0);
-    scrollbarThickness = ScrollbarTheme::theme()->scrollbarThickness(RegularScrollbar);
-    scrollbarMargin = ScrollbarTheme::theme()->scrollbarMargin();
-#endif
+    ScrollbarTheme* theme = ScrollbarThemeOverlay::mobileTheme();
+    int thumbThickness = theme->thumbThickness(0);
+    int scrollbarThickness = theme->scrollbarThickness(RegularScrollbar);
+    int scrollbarMargin = theme->scrollbarMargin();
 
     if (!webScrollbarLayer) {
         ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator();
@@ -370,7 +372,6 @@ void VisualViewport::setupScrollbar(WebScrollbar::Orientation orientation)
         // The compositor will control the scrollbar's visibility. Set to invisible by defualt
         // so scrollbars don't show up in layout tests.
         webScrollbarLayer->layer()->setOpacity(0);
-
         scrollbarGraphicsLayer->setContentsToPlatformLayer(webScrollbarLayer->layer());
         scrollbarGraphicsLayer->setDrawsContent(false);
     }
@@ -409,6 +410,14 @@ void VisualViewport::registerLayersWithTreeView(WebLayerTreeView* layerTreeView)
         m_pageScaleLayer->platformLayer(),
         m_innerViewportScrollLayer->platformLayer(),
         scrollLayer);
+
+    // TODO(aelias): Remove this call after this setting is deleted.
+    layerTreeView->setHidePinchScrollbarsNearMinScale(false);
+}
+
+bool VisualViewport::visualViewportSuppliesScrollbars() const
+{
+    return frameHost().settings().viewportMetaEnabled();
 }
 
 void VisualViewport::clearLayersForTreeView(WebLayerTreeView* layerTreeView) const

third_party/WebKit/Source/core/frame/VisualViewport.h

@@ -87,6 +87,8 @@ public:
         return m_innerViewportScrollLayer.get();
     }
 
+    void initializeScrollbars();
+
     // Sets the location of the visual viewport relative to the outer viewport. The
     // coordinates are in partial CSS pixels.
     void setLocation(const FloatPoint&);
@@ -195,6 +197,8 @@ public:
 private:
     explicit VisualViewport(FrameHost&);
 
+    bool visualViewportSuppliesScrollbars() const;
+
     // GraphicsLayerClient implementation.
     void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect& inClip) override;
     String debugName(const GraphicsLayer*) override;

third_party/WebKit/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp

@@ -30,6 +30,7 @@
 #include "core/HTMLNames.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/fetch/ImageResource.h"
+#include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/RemoteFrame.h"
 #include "core/html/HTMLCanvasElement.h"
@@ -1070,6 +1071,8 @@ void CompositedDeprecatedPaintLayerMapping::updateInternalHierarchy()
 
     // Now constructing the subtree for the overflow controls.
     bottomLayer = m_graphicsLayer.get();
+    if (m_isMainFrameLayoutViewLayer)
+        bottomLayer = layoutObject()->frame()->page()->frameHost().visualViewport().containerLayer();
     updateBottomLayer(m_overflowControlsClippingLayer.get());
     updateBottomLayer(m_overflowControlsHostLayer.get());
     if (m_layerForHorizontalScrollbar)

third_party/WebKit/Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp

@@ -907,14 +907,12 @@ bool DeprecatedPaintLayerCompositor::requiresScrollCornerLayer() const
 void DeprecatedPaintLayerCompositor::updateOverflowControlsLayers()
 {
     GraphicsLayer* controlsParent = m_rootTransformLayer.get() ? m_rootTransformLayer.get() : m_overflowControlsHostLayer.get();
-    // On Mac, main frame scrollbars should always be stuck to the sides of the screen (in overscroll and in pinch-zoom), so
+    // Main frame scrollbars should always be stuck to the sides of the screen (in overscroll and in pinch-zoom), so
     // make the parent for the scrollbars be the viewport container layer.
-#if OS(MACOSX)
     if (m_layoutView.frame()->isMainFrame()) {
         VisualViewport& visualViewport = m_layoutView.frameView()->page()->frameHost().visualViewport();
         controlsParent = visualViewport.containerLayer();
     }
-#endif
 
     if (requiresHorizontalScrollbarLayer()) {
         if (!m_layerForHorizontalScrollbar) {

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

@@ -381,8 +381,8 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
         }
 
         WebLayer* scrollLayer = toWebLayer(scrollableArea->layerForScrolling());
-        WebLayer* containerLayer = toWebLayer(scrollableArea->layerForContainer());
-        setupScrollbarLayer(scrollbarGraphicsLayer, scrollbarLayer, scrollLayer, containerLayer);
+        WebLayer* scrollbarContainerLayer = toWebLayer(scrollableArea->layerForScrollbarContainer());
+        setupScrollbarLayer(scrollbarGraphicsLayer, scrollbarLayer, scrollLayer, scrollbarContainerLayer);
 
         // Root layer non-overlay scrollbars should be marked opaque to disable
         // blending.
@@ -403,6 +403,7 @@ bool ScrollingCoordinator::scrollableAreaScrollLayerDidChange(ScrollableArea* sc
 
     WebLayer* webLayer = toWebLayer(scrollableArea->layerForScrolling());
     WebLayer* containerLayer = toWebLayer(scrollableArea->layerForContainer());
+    WebLayer* scrollbarContainerLayer = toWebLayer(scrollableArea->layerForScrollbarContainer());
     if (webLayer) {
         webLayer->setScrollClipLayer(containerLayer);
         // Non-layered Viewport constrained objects, e.g. fixed position elements, are
@@ -431,12 +432,13 @@ bool ScrollingCoordinator::scrollableAreaScrollLayerDidChange(ScrollableArea* sc
     if (WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, HorizontalScrollbar)) {
         GraphicsLayer* horizontalScrollbarLayer = scrollableArea->layerForHorizontalScrollbar();
         if (horizontalScrollbarLayer)
-            setupScrollbarLayer(horizontalScrollbarLayer, scrollbarLayer, webLayer, containerLayer);
+            setupScrollbarLayer(horizontalScrollbarLayer, scrollbarLayer, webLayer, scrollbarContainerLayer);
     }
     if (WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, VerticalScrollbar)) {
         GraphicsLayer* verticalScrollbarLayer = scrollableArea->layerForVerticalScrollbar();
+
         if (verticalScrollbarLayer)
-            setupScrollbarLayer(verticalScrollbarLayer, scrollbarLayer, webLayer, containerLayer);
+            setupScrollbarLayer(verticalScrollbarLayer, scrollbarLayer, webLayer, scrollbarContainerLayer);
     }
 
     // Update the viewport layer registration if the outer viewport may have changed.

third_party/WebKit/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

@@ -49,6 +49,7 @@
 #include "core/dom/Node.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/editing/FrameSelection.h"
+#include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
@@ -170,6 +171,13 @@ HostWindow* DeprecatedPaintLayerScrollableArea::hostWindow() const
     return nullptr;
 }
 
+GraphicsLayer* DeprecatedPaintLayerScrollableArea::layerForScrollbarContainer() const
+{
+    if (layer()->isRootLayer())
+        return box().frame()->host()->visualViewport().layerForScrollbarContainer();
+    return layerForContainer();
+}
+
 GraphicsLayer* DeprecatedPaintLayerScrollableArea::layerForScrolling() const
 {
     return layer()->hasCompositedDeprecatedPaintLayerMapping() ? layer()->compositedDeprecatedPaintLayerMapping()->scrollingContentsLayer() : 0;

third_party/WebKit/Source/core/paint/DeprecatedPaintLayerScrollableArea.h

@@ -85,6 +85,7 @@ public:
 
     HostWindow* hostWindow() const override;
 
+    GraphicsLayer* layerForScrollbarContainer() const override;
     GraphicsLayer* layerForScrolling() const override;
     GraphicsLayer* layerForHorizontalScrollbar() const override;
     GraphicsLayer* layerForVerticalScrollbar() const override;

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

@@ -259,6 +259,7 @@ public:
     }
 
     virtual GraphicsLayer* layerForContainer() const;
+    virtual GraphicsLayer* layerForScrollbarContainer() const { return layerForContainer(); }
     virtual GraphicsLayer* layerForScrolling() const { return 0; }
     virtual GraphicsLayer* layerForHorizontalScrollbar() const { return 0; }
     virtual GraphicsLayer* layerForVerticalScrollbar() const { return 0; }

third_party/WebKit/Source/platform/scroll/ScrollbarThemeAndroid.cpp

@@ -32,8 +32,7 @@ namespace blink {
 
 ScrollbarTheme* ScrollbarTheme::nativeTheme()
 {
-    DEFINE_STATIC_LOCAL(ScrollbarThemeOverlay, theme, (3, 3, ScrollbarThemeOverlay::DisallowHitTest, Color(128, 128, 128, 128)));
-    return &theme;
+    return ScrollbarThemeOverlay::mobileTheme();
 }
 
 } // namespace blink

third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp

@@ -170,4 +170,10 @@ ScrollbarPart ScrollbarThemeOverlay::hitTest(ScrollbarThemeClient* scrollbar, co
     return ScrollbarTheme::hitTest(scrollbar, position);
 }
 
+ScrollbarTheme* ScrollbarThemeOverlay::mobileTheme()
+{
+    DEFINE_STATIC_LOCAL(ScrollbarThemeOverlay, theme, (3, 3, ScrollbarThemeOverlay::DisallowHitTest, Color(128, 128, 128, 128)));
+    return &theme;
+}
+
 } // namespace blink

third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h

@@ -59,6 +59,8 @@ public:
     void paintThumb(GraphicsContext*, ScrollbarThemeClient*, const IntRect&) override;
     ScrollbarPart hitTest(ScrollbarThemeClient*, const IntPoint&) override;
 
+    static ScrollbarTheme* mobileTheme();
+
 private:
     int m_thumbThickness;
     int m_scrollbarMargin;

third_party/WebKit/Source/web/DevToolsEmulator.cpp

@@ -5,6 +5,7 @@
 #include "config.h"
 #include "web/DevToolsEmulator.h"
 
+#include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/page/Page.h"
@@ -213,6 +214,7 @@ void DevToolsEmulator::enableMobileEmulation()
     RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(true);
     m_webViewImpl->enableViewport();
     m_webViewImpl->settings()->setViewportMetaEnabled(true);
+    m_webViewImpl->page()->frameHost().visualViewport().initializeScrollbars();
     m_webViewImpl->settings()->setShrinksViewportContentToFit(true);
     m_webViewImpl->page()->settings().setTextAutosizingEnabled(true);
     m_webViewImpl->page()->settings().setPreferCompositingToLCDTextEnabled(true);
@@ -223,8 +225,6 @@ void DevToolsEmulator::enableMobileEmulation()
     m_originalDefaultMinimumPageScaleFactor = m_webViewImpl->defaultMinimumPageScaleFactor();
     m_originalDefaultMaximumPageScaleFactor = m_webViewImpl->defaultMaximumPageScaleFactor();
     m_webViewImpl->setDefaultPageScaleLimits(0.25f, 5);
-    if (m_webViewImpl->layerTreeView())
-        m_webViewImpl->layerTreeView()->setHidePinchScrollbarsNearMinScale(false);
 }
 
 void DevToolsEmulator::disableMobileEmulation()
@@ -234,6 +234,7 @@ void DevToolsEmulator::disableMobileEmulation()
     RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(m_isOverlayScrollbarsEnabled);
     m_webViewImpl->disableViewport();
     m_webViewImpl->settings()->setViewportMetaEnabled(false);
+    m_webViewImpl->page()->frameHost().visualViewport().initializeScrollbars();
     m_webViewImpl->settings()->setShrinksViewportContentToFit(false);
     m_webViewImpl->page()->settings().setTextAutosizingEnabled(m_embedderTextAutosizingEnabled);
     m_webViewImpl->page()->settings().setPreferCompositingToLCDTextEnabled(m_embedderPreferCompositingToLCDTextEnabled);
@@ -244,10 +245,6 @@ void DevToolsEmulator::disableMobileEmulation()
     m_webViewImpl->setDefaultPageScaleLimits(
         m_originalDefaultMinimumPageScaleFactor,
         m_originalDefaultMaximumPageScaleFactor);
-    if (m_webViewImpl->layerTreeView()) {
-        m_webViewImpl->layerTreeView()->setHidePinchScrollbarsNearMinScale(
-            m_hidePinchScrollbarsNearMinScale);
-    }
 }
 
 void DevToolsEmulator::setTouchEventEmulationEnabled(bool enabled)