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

cc/resources/gpu_rasterizer.cc

Index: cc/resources/gpu_rasterizer.cc
diff --git a/cc/resources/gpu_rasterizer.cc b/cc/resources/gpu_rasterizer.cc
index 6e318edabbe80a2c670eef3baf96abf9dd36d990..9adce07072454c6fb3b7f749af2bc4f98e65190a 100644
--- a/cc/resources/gpu_rasterizer.cc
+++ b/cc/resources/gpu_rasterizer.cc
@@ -120,9 +120,13 @@ void GpuRasterizer::RasterizeSource(
     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();
   }