Add a flag to disable partial raster in renderer

ui/compositor/compositor.cc

 // 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 "ui/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 122 matching lines @@
       command_line->HasSwitch(cc::switches::kUIShowReplicaScreenSpaceRects);
 
   settings.initial_debug_state.SetRecordRenderingStats(
       command_line->HasSwitch(cc::switches::kEnableGpuBenchmarking));
 
   settings.use_zero_copy = IsUIZeroCopyEnabled();
 
   settings.renderer_settings.use_rgba_4444_textures =
       command_line->HasSwitch(switches::kUIEnableRGBA4444Textures);
 
-  // Use PERSISTENT_MAP memory buffers to support partial tile raster for
-  // software raster into GpuMemoryBuffers.
-  gfx::BufferUsage usage = gfx::BufferUsage::PERSISTENT_MAP;
-  settings.use_persistent_map_for_gpu_memory_buffers = true;
+  // UI compositor always uses partial raster if not using zero-copy. Zero copy
+  // doesn't currently support partial raster.
+  settings.use_partial_raster = !settings.use_zero_copy;
+
+  // Use PERSISTENT_MAP memory buffers to support partial tile raster if needed.
+  gfx::BufferUsage usage = settings.use_partial_raster
+                               ? gfx::BufferUsage::PERSISTENT_MAP
+                               : gfx::BufferUsage::MAP;
 
   for (size_t format = 0;
       format < static_cast<size_t>(gfx::BufferFormat::LAST) + 1; format++) {
     DCHECK_GT(settings.use_image_texture_targets.size(), format);
     settings.use_image_texture_targets[format] =
         context_factory_->GetImageTextureTarget(
             static_cast<gfx::BufferFormat>(format), usage);
   }
 
   // Note: Only enable image decode tasks if we have more than one worker
@@ skipping 330 matching lines @@
                     observer_list_,
                     OnCompositingLockStateChanged(this));
 }
 
 void Compositor::CancelCompositorLock() {
   if (compositor_lock_)
     compositor_lock_->CancelLock();
 }
 
 }  // namespace ui