Create Pinch Virtual Viewport scrollbar layers in Blink.

Source/web/PinchViewports.cpp

Index: Source/web/PinchViewports.cpp
diff --git a/Source/web/PinchViewports.cpp b/Source/web/PinchViewports.cpp
index e0ec3f47cdb8a2287c13c41aeae93de1320f3716..7513d973c261e667118ec4bd58ad98278df4c3c1 100644
--- a/Source/web/PinchViewports.cpp
+++ b/Source/web/PinchViewports.cpp
@@ -35,11 +35,14 @@
 #include "WebViewImpl.h"
 #include "core/page/Frame.h"
 #include "core/page/FrameView.h"
+#include "core/page/scrolling/ScrollingCoordinator.h"
+#include "core/platform/Scrollbar.h"
 #include "core/platform/graphics/FloatSize.h"
 #include "core/platform/graphics/GraphicsLayer.h"
 #include "core/rendering/RenderLayerCompositor.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
+#include "public/platform/WebLayer.h"
 #include "public/platform/WebLayerTreeView.h"
 #include "public/platform/WebScrollbarLayer.h"
 
@@ -67,7 +70,7 @@ PinchViewports::PinchViewports(WebViewImpl* owner)
     m_innerViewportContainerLayer->setMasksToBounds(false);
 
     m_innerViewportScrollLayer->platformLayer()->setScrollable(true);
-
+    m_innerViewportScrollLayer->platformLayer()->setScrollClipLayer(m_innerViewportContainerLayer->platformLayer());
 
     m_innerViewportContainerLayer->addChild(m_pageScaleLayer.get());
     m_pageScaleLayer->addChild(m_innerViewportScrollLayer.get());
@@ -136,9 +139,22 @@ void PinchViewports::setupScrollbar(WebScrollbar::Orientation orientation)
     bool isHorizontal = orientation == WebScrollbar::Horizontal;
     GraphicsLayer* scrollbarGraphicsLayer = isHorizontal ?
         m_overlayScrollbarHorizontal.get() : m_overlayScrollbarVertical.get();
+    OwnPtr<WebScrollbarLayer>& webScrollbarLayer = isHorizontal ?
+        m_webOverlayScrollbarHorizontal : m_webOverlayScrollbarVertical;
 
     const int overlayScrollbarThickness = m_owner->settingsImpl()->pinchOverlayScrollbarThickness();
 
+    if (!webScrollbarLayer) {
+        WebCore::ScrollingCoordinator* coordinator = m_owner->page()->scrollingCoordinator();
+        ASSERT(coordinator);
+        WebCore::ScrollbarOrientation webcoreOrientation = isHorizontal ? WebCore::HorizontalScrollbar : WebCore::VerticalScrollbar;
+        webScrollbarLayer = coordinator->createSolidColorScrollbarLayer(webcoreOrientation, overlayScrollbarThickness);
+
+        webScrollbarLayer->setScrollLayer(m_innerViewportScrollLayer->platformLayer());
+        scrollbarGraphicsLayer->setContentsToPlatformLayer(webScrollbarLayer->layer());
+        scrollbarGraphicsLayer->setDrawsContent(false);
+    }
+
     int xPosition = isHorizontal ? 0 : m_innerViewportContainerLayer->size().width() - overlayScrollbarThickness;
     int yPosition = isHorizontal ? m_innerViewportContainerLayer->size().height() - overlayScrollbarThickness : 0;
     int width = isHorizontal ? m_innerViewportContainerLayer->size().width() - overlayScrollbarThickness : overlayScrollbarThickness;
@@ -150,26 +166,25 @@ void PinchViewports::setupScrollbar(WebScrollbar::Orientation orientation)
 
 void PinchViewports::registerViewportLayersWithTreeView(WebLayerTreeView* layerTreeView) const
 {
-    if (!layerTreeView)
-        return;
+    ASSERT(layerTreeView);
 
     WebCore::RenderLayerCompositor* compositor = m_owner->compositor();
+    GraphicsLayer* scrollLayer = compositor->scrollLayer();
+    GraphicsLayer* clipLayer = compositor->rootGraphicsLayer();
+    scrollLayer->platformLayer()->setScrollClipLayer(clipLayer->platformLayer());
+
     ASSERT(compositor);
-    layerTreeView->registerPinchViewportLayers(
-        m_innerViewportContainerLayer->platformLayer(),
+    layerTreeView->registerViewportLayers(
         m_pageScaleLayer->platformLayer(),
         m_innerViewportScrollLayer->platformLayer(),
-        compositor->scrollLayer()->platformLayer(),
-        m_overlayScrollbarHorizontal->platformLayer(),
-        m_overlayScrollbarVertical->platformLayer());
+        scrollLayer->platformLayer());
 }
 
 void PinchViewports::clearViewportLayersForTreeView(WebLayerTreeView* layerTreeView) const
 {
-    if (!layerTreeView)
-        return;
+    ASSERT(layerTreeView);
 
-    layerTreeView->clearPinchViewportLayers();
+    layerTreeView->clearViewportLayers();
 }
 
 void PinchViewports::notifyAnimationStarted(const GraphicsLayer*, double time)