Support single-threaded impl-side painting

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 259 matching lines @@
           hide_threshold >= 0.f && hide_threshold <= 1.f)
         settings.top_controls_hide_threshold = hide_threshold;
   }
 
   settings.use_pinch_virtual_viewport =
       cmd->HasSwitch(cc::switches::kEnablePinchVirtualViewport);
   settings.allow_antialiasing &=
       !cmd->HasSwitch(cc::switches::kDisableCompositedAntialiasing);
   settings.single_thread_proxy_scheduler =
       !cmd->HasSwitch(switches::kDisableSingleThreadProxyScheduler);
+  if (!threaded && !settings.single_thread_proxy_scheduler &&
+      settings.impl_side_painting) {
+    // The synchronous composite path requires zero copy with impl-side
+    // painting.
+    settings.use_zero_copy = true;
+    settings.scheduled_raster_task_limit = std::numeric_limits<size_t>::max();
+  }
 
   // These flags should be mirrored by UI versions in ui/compositor/.
   settings.initial_debug_state.show_debug_borders =
       cmd->HasSwitch(cc::switches::kShowCompositedLayerBorders);
   settings.initial_debug_state.show_fps_counter =
       cmd->HasSwitch(cc::switches::kShowFPSCounter);
   settings.initial_debug_state.show_layer_animation_bounds_rects =
       cmd->HasSwitch(cc::switches::kShowLayerAnimationBounds);
   settings.initial_debug_state.show_paint_rects =
       cmd->HasSwitch(switches::kShowPaintRects);
@@ skipping 581 matching lines @@
   widget_->OnSwapBuffersAborted();
 }
 
 void RenderWidgetCompositor::RateLimitSharedMainThreadContext() {
   cc::ContextProvider* provider =
       RenderThreadImpl::current()->SharedMainThreadContextProvider().get();
   provider->ContextGL()->RateLimitOffscreenContextCHROMIUM();
 }
 
 }  // namespace content