Implementing document.setRootScroller API for main thread scrolling.

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

Index: third_party/WebKit/Source/core/frame/FrameHost.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameHost.cpp b/third_party/WebKit/Source/core/frame/FrameHost.cpp
index 9d05d9d0ea0a8c3ed5703852b957e717af1a7e4e..42b04597cdb74720db1c04f869e1e4a14875e0ae 100644
--- a/third_party/WebKit/Source/core/frame/FrameHost.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameHost.cpp
@@ -38,6 +38,7 @@
 #include "core/inspector/ConsoleMessageStorage.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/OverscrollController.h"
+#include "core/page/scrolling/RootScroller.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebScheduler.h"
 
@@ -50,6 +51,7 @@ FrameHost* FrameHost::create(Page& page)
 
 FrameHost::FrameHost(Page& page)
     : m_page(&page)
+    , m_rootScroller(RootScroller::create(*this))
     , m_topControls(TopControls::create(*this))
     , m_pageScaleConstraintsSet(PageScaleConstraintsSet::create())
     , m_visualViewport(VisualViewport::create(*this))
@@ -122,6 +124,26 @@ float FrameHost::deviceScaleFactor() const
     return m_page->deviceScaleFactor();
 }
 
+RootScroller* FrameHost::rootScroller()
+{
+    // RootScroller only makes sense if we're in the process where the main
+    // frame is local.
+    if (!m_page->mainFrame() || !m_page->mainFrame()->isLocalFrame())
+        return nullptr;
+
+    return m_rootScroller;
+}
+
+const RootScroller* FrameHost::rootScroller() const
+{
+    // RootScroller only makes sense if we're in the process where the main
+    // frame is local.
+    if (!m_page->mainFrame() || !m_page->mainFrame()->isLocalFrame())
+        return nullptr;
+
+    return m_rootScroller;
+}
+
 TopControls& FrameHost::topControls()
 {
     return *m_topControls;
@@ -185,6 +207,7 @@ const ConsoleMessageStorage& FrameHost::consoleMessageStorage() const
 DEFINE_TRACE(FrameHost)
 {
     visitor->trace(m_page);
+    visitor->trace(m_rootScroller);
     visitor->trace(m_topControls);
     visitor->trace(m_visualViewport);
     visitor->trace(m_overscrollController);