Abort canvas analysis after a few operations are rejected

cc/playback/raster_source.cc

Index: cc/playback/raster_source.cc
diff --git a/cc/playback/raster_source.cc b/cc/playback/raster_source.cc
index 0dc9c6c520cc2dcddf0e10b67562b76c795f80b7..c33b169cd3d6daad0aafb80ad4c8776804d880aa 100644
--- a/cc/playback/raster_source.cc
+++ b/cc/playback/raster_source.cc
@@ -224,6 +224,9 @@ bool RasterSource::PerformSolidColorAnalysis(const gfx::Rect& content_rect,
                                              SkColor* color) const {
   TRACE_EVENT0("cc", "RasterSource::PerformSolidColorAnalysis");
 
+  if (!display_list_->ShouldBeAnalyzedForSolidColor())

[vmpstr, 2016/10/18 23:31:33]

That's not quite correct, since the given content_rect may actually clip out a
lot of the operations and still find a solid color tile. This patch would make
it so that no tile is ever solid color on a page with enough operations
anywhere.

I think I can construct a page that has blank content at the top and some
content (enough for for ShouldBeAnalyzedForSolidColor to be false) below that.
Then this would prevent solid color analysis to be done on tiles above. 

[Xianzhu, 2016/10/19 01:27:53]

For my test, this does avoid big cost when analyzing a display list containing
hundreds of thousands of operations. It takes 30ms to analyze each tile.

How bad is it when we treat a solid-color tile non-solid-color? Can we use a
different threshold for tile solid-color analysis (for example, 1000
operations)?

+    return false;
+
   gfx::Rect layer_rect =
       gfx::ScaleToEnclosingRect(content_rect, 1.0f / contents_scale);