Reland of place pinch scrollbars with regular scrollbars.

Source/core/frame/VisualViewport.cpp

Index: Source/core/frame/VisualViewport.cpp
diff --git a/Source/core/frame/VisualViewport.cpp b/Source/core/frame/VisualViewport.cpp
index 95c5d1416348fae715a163656e7097708bdb2ab6..e2661c0d9c595e930e29754d8bf0e6c6bbd6bf2a 100644
--- a/Source/core/frame/VisualViewport.cpp
+++ b/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 @@
         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 @@
 //  |                   +-- 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)
 {
@@ -324,19 +321,31 @@
         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)
@@ -347,17 +356,10 @@
     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 @@
         // 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 @@
         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