cc: Add diagnostic CHECKs to investigate crashes

There are some mysterious crashes in PlaybackFoldingIterator that I
suspect are coming from bogus PaintOpBuffers.

Bug: 823835
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iabfa7d619a7dbb59e9b453d161e6dd7ca259795e
Reviewed-on: https://chromium-review.googlesource.com/974444Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544918}

cc/paint/paint_op_buffer.cc

@@ -1236,6 +1236,8 @@ void DrawRecordOp::Raster(const DrawRecordOp* op,
                           SkCanvas* canvas,
                           const PlaybackParams& params) {
   // Don't use drawPicture here, as it adds an implicit clip.
+  // TODO(enne): Temporary CHECK debugging for http://crbug.com/823835
+  CHECK(op->record);
   op->record->Playback(canvas, params);
 }
 

cc/raster/raster_source.cc

@@ -162,7 +162,8 @@ void RasterSource::PlaybackToCanvas(
 
 void RasterSource::PlaybackToCanvas(SkCanvas* raster_canvas,
                                     ImageProvider* image_provider) const {
-  DCHECK(display_list_.get());
+  // TODO(enne): Temporary CHECK debugging for http://crbug.com/823835
+  CHECK(display_list_.get());
   int repeat_count = std::max(1, slow_down_raster_scale_factor_for_debug_);
   for (int i = 0; i < repeat_count; ++i)
     display_list_->Raster(raster_canvas, image_provider);