Add --root-layer-scrolls.

BUG=417782

Review URL: https://codereview.chromium.org/662973003

Cr-Commit-Position: refs/heads/master@{#302588}

chrome/browser/chromeos/login/chrome_restart_request.cc

@@ -132,6 +132,7 @@ std::string DeriveCommandLine(const GURL& start_url,
     ::switches::kPpapiFlashVersion,
     ::switches::kPpapiInProcess,
     ::switches::kRendererStartupDialog,
+    ::switches::kRootLayerScrolls,
     ::switches::kEnableShareGroupAsyncTextureUpload,
     ::switches::kTabCaptureUpscaleQuality,
     ::switches::kTabCaptureDownscaleQuality,

content/browser/renderer_host/render_process_host_impl.cc

@@ -1175,6 +1175,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kRegisterPepperPlugins,
     switches::kRendererAssertTest,
     switches::kRendererStartupDialog,
+    switches::kRootLayerScrolls,
     switches::kShowPaintRects,
     switches::kSitePerProcess,
     switches::kStatsCollectionController,

content/public/common/content_switches.cc

@@ -715,6 +715,9 @@ const char kRendererProcessLimit[]          = "renderer-process-limit";
 // Causes the renderer process to display a dialog on launch.
 const char kRendererStartupDialog[]         = "renderer-startup-dialog";
 
+// Handles frame scrolls via the root RenderLayer instead of the FrameView.
+const char kRootLayerScrolls[]              = "root-layer-scrolls";
+
 // Causes the process to run as a sandbox IPC subprocess.
 const char kSandboxIPCProcess[]             = "sandbox-ipc";
 

content/public/common/content_switches.h

@@ -203,6 +203,7 @@ extern const char kRendererCmdPrefix[];
 CONTENT_EXPORT extern const char kRendererProcess[];
 CONTENT_EXPORT extern const char kRendererProcessLimit[];
 CONTENT_EXPORT extern const char kRendererStartupDialog[];
+extern const char kRootLayerScrolls[];
 extern const char kSandboxIPCProcess[];
 CONTENT_EXPORT extern const char kScrollEndEffect[];
 extern const char kShowPaintRects[];

content/renderer/render_view_impl.cc

@@ -751,6 +751,8 @@ void RenderViewImpl::Initialize(RenderViewImplParams* params) {
       ShouldUseTransitionCompositing(device_scale_factor_));
   webview()->settings()->setThreadedScrollingEnabled(
       !command_line.HasSwitch(switches::kDisableThreadedScrolling));
+  webview()->settings()->setRootLayerScrolls(
+      command_line.HasSwitch(switches::kRootLayerScrolls));
 
   ApplyWebPreferences(webkit_preferences_, webview());