ui/compositor: Enable image decode tasks in the UI compositor.

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 <stddef.h>
 
 #include <algorithm>
 #include <deque>
@@ skipping 168 matching lines @@
     for (int format_idx = 0;
          format_idx <= static_cast<int>(gfx::BufferFormat::LAST);
          ++format_idx) {
       gfx::BufferFormat format = static_cast<gfx::BufferFormat>(format_idx);
       uint32_t target = context_factory_->GetImageTextureTarget(format, usage);
       settings.renderer_settings
           .buffer_to_texture_target_map[std::make_pair(usage, format)] = target;
     }
   }
 
-  // Note: Only enable image decode tasks if we have more than one worker
-  // thread.
-  settings.image_decode_tasks_enabled = false;
+  // Note: Although there is only one image decode thread, we should still get a
+  // benefit from locking images across several raster tasks. At worst, this
+  // should do as much work as it would anyway.
+  settings.image_decode_tasks_enabled = true;
 
   settings.gpu_memory_policy.bytes_limit_when_visible = 512 * 1024 * 1024;
   settings.gpu_memory_policy.priority_cutoff_when_visible =
       gpu::MemoryAllocation::CUTOFF_ALLOW_NICE_TO_HAVE;
 
   base::TimeTicks before_create = base::TimeTicks::Now();
 
   animation_host_ = cc::AnimationHost::CreateMainInstance();
 
   cc::LayerTreeHost::InitParams params;
@@ skipping 368 matching lines @@
   for (auto& observer : observer_list_)
     observer.OnCompositingLockStateChanged(this);
 }
 
 void Compositor::CancelCompositorLock() {
   if (compositor_lock_)
     compositor_lock_->CancelLock();
 }
 
 }  // namespace ui