Allow ui::Compositor to disable commits during tab-switch

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
 
@@ skipping 597 matching lines @@
     browser_compositor_->compositor()->SetHostHasTransparentBackground(
         !GetBackgroundOpaque());
     browser_compositor_->accelerated_widget_mac()->SetNSView(this);
     browser_compositor_state_ = BrowserCompositorSuspended;
   }
 
   // Show the DelegatedFrameHost to transition from Suspended -> Active.
   if (browser_compositor_state_ == BrowserCompositorSuspended) {
     delegated_frame_host_->SetCompositor(browser_compositor_->compositor());
     delegated_frame_host_->WasShown(ui::LatencyInfo());
+    // Unsuspend the browser compositor after showing the delegated frame host.
+    // If there is not a saved delegated frame, then the delegated frame host
+    // will keep the compositor locked until a delegated frame is swapped.
+    float scale_factor = ViewScaleFactor();
+    browser_compositor_->compositor()->SetScaleAndSize(
+        scale_factor,
+        gfx::ConvertSizeToPixel(scale_factor, GetViewBounds().size()));
+    browser_compositor_->Unsuspend();
     browser_compositor_state_ = BrowserCompositorActive;
   }
 }
 
 void RenderWidgetHostViewMac::SuspendBrowserCompositorView() {
   TRACE_EVENT0("browser",
                "RenderWidgetHostViewMac::SuspendBrowserCompositorView");
 
   // Hide the DelegatedFrameHost to transition from Active -> Suspended.
   if (browser_compositor_state_ == BrowserCompositorActive) {
+    // Ensure that any changes made to the ui::Compositor do not result in new
+    // frames being produced.
+    browser_compositor_->Suspend();
     // Marking the DelegatedFrameHost as removed from the window hierarchy is
     // necessary to remove all connections to its old ui::Compositor.
     delegated_frame_host_->WasHidden();
     delegated_frame_host_->ResetCompositor();
     browser_compositor_state_ = BrowserCompositorSuspended;
   }
 }
 
 void RenderWidgetHostViewMac::DestroyBrowserCompositorView() {
   TRACE_EVENT0("browser",
@@ skipping 189 matching lines @@
 RenderWidgetHost* RenderWidgetHostViewMac::GetRenderWidgetHost() const {
   return render_widget_host_;
 }
 
 void RenderWidgetHostViewMac::Show() {
   ScopedCAActionDisabler disabler;
   [cocoa_view_ setHidden:NO];
   if (!render_widget_host_->is_hidden())
     return;
 
+  EnsureBrowserCompositorView();

[danakj, 2015/03/12 00:07:15]

How come this is needed?

[ccameron, 2015/03/12 01:01:34]

Oh -- I added the explanation to the CL description, but to any comments:

  Also, re-create the browser compositor immediately after the tab is made
  visible. This way, if the DelegatedFrameHost has an un-evicted old frame,
  then that frame will be displayed immediately (and if not, the compositor
  will remain locked until a new frame is swapped in).

Also added a comment to this effect.

[danakj, 2015/03/12 01:08:50]

Thanks :)

   WasUnOccluded();
 
   // If there is not a frame being currently drawn, kick one, so that the below
   // pause will have a frame to wait on.
   render_widget_host_->ScheduleComposite();
   PauseForPendingResizeOrRepaintsAndDraw();
 }
 
 void RenderWidgetHostViewMac::Hide() {
   ScopedCAActionDisabler disabler;
@@ skipping 2586 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end