cc: Avoid extra flush calls to Skia GrContext

cc/output/gl_renderer.cc

 // Copyright 2010 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 "cc/output/gl_renderer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 637 matching lines @@
   SkMatrix local_matrix;
   local_matrix.setScale(scale.x(), scale.y());
   skia::RefPtr<SkImageFilter> filter_with_local_scale =
       skia::AdoptRef(filter->newWithLocalMatrix(local_matrix));
 
   SkPaint paint;
   paint.setImageFilter(filter_with_local_scale.get());
   surface->getCanvas()->translate(-dst_rect.x(), -dst_rect.y());
   surface->getCanvas()->drawImage(srcImage.get(), src_rect.x(), src_rect.y(),
                                   &paint);
-
+  // Flush the drawing before source texture read lock goes out of scope.
+  // Skia API does not guarantee that when the SkImage goes out of scope,
+  // its externally referenced resources would force the rendering to be
+  // flushed.
+  surface->getCanvas()->flush();
   skia::RefPtr<SkImage> image = skia::AdoptRef(surface->newImageSnapshot());
   if (!image || !image->isTextureBacked()) {
     return skia::RefPtr<SkImage>();
   }
 
   CHECK(image->isTextureBacked());
   return image;
 }
 
 bool GLRenderer::CanApplyBlendModeUsingBlendFunc(SkXfermode::Mode blend_mode) {
@@ skipping 2952 matching lines @@
       texture_id = pending_overlay_resources_.back()->texture_id();
     }
 
     context_support_->ScheduleOverlayPlane(
         overlay.plane_z_order, overlay.transform, texture_id,
         ToNearestRect(overlay.display_rect), overlay.uv_rect);
   }
 }
 
 }  // namespace cc