gpu-raster: Check for NULL sk_surface in GpuRasterizer::RasterizeSource.

cc/resources/gpu_rasterizer.cc

 // Copyright 2015 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/resources/gpu_rasterizer.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/metrics/histogram.h"
@@ skipping 102 matching lines @@
   bool use_distance_field_text =
       use_distance_field_text_ ||
       raster_source->ShouldAttemptToUseDistanceFieldText();
 
   // Playback picture into resource.
   {
     ScopedGpuRaster gpu_raster(GetContextProvider(use_worker_context));
     write_lock->InitSkSurface(use_worker_context, use_distance_field_text,
                               raster_source->CanUseLCDText(),
                               msaa_sample_count_);
+
+    SkSurface* sk_surface = write_lock->sk_surface();
+    if (!sk_surface)

[danakj, 2015/03/09 16:38:03]

Can you add a comment explaining this is for lost context case since it's not
obvious?

[vmiura, 2015/03/09 18:01:26]

Done.

+      return;
+
     SkMultiPictureDraw multi_picture_draw;
-    multi_picture_draw.add(write_lock->sk_surface()->getCanvas(),
-                           picture.get());
+    multi_picture_draw.add(sk_surface->getCanvas(), picture.get());
     multi_picture_draw.draw(msaa_sample_count_ > 0);
     write_lock->ReleaseSkSurface();
   }
 }
 
 void GpuRasterizer::PerformSolidColorAnalysis(
     const Tile* tile,
     RasterSource::SolidColorAnalysis* analysis) {
   const void* tile_id = static_cast<const void*>(tile);
   frame_viewer_instrumentation::ScopedAnalyzeTask analyze_task(
@@ skipping 49 matching lines @@
   tile->raster_source()->PlaybackToCanvas(canvas.get(), tile->content_rect(),
                                           tile->contents_scale());
   canvas->restore();
 
   // Add the canvas and recorded picture to |multi_picture_draw_|.
   skia::RefPtr<SkPicture> picture = skia::AdoptRef(recorder.endRecording());
   multi_picture_draw_.add(sk_surface->getCanvas(), picture.get());
 }
 
 }  // namespace cc