Force use of and cache render surface.

cc/output/direct_renderer.cc

Index: cc/output/direct_renderer.cc
diff --git a/cc/output/direct_renderer.cc b/cc/output/direct_renderer.cc
index 19c0e4ab7ed6e054300ae4ae83e7a62e014fcc85..dccd57c902728a6b267b3b2bfc44e12c7f962fcc 100644
--- a/cc/output/direct_renderer.cc
+++ b/cc/output/direct_renderer.cc
@@ -618,6 +618,9 @@ bool DirectRenderer::UseRenderPass(const RenderPass* render_pass) {
     texture->Allocate(
         size, ResourceProvider::TEXTURE_HINT_IMMUTABLE_FRAMEBUFFER,
         BackbufferFormat(), current_frame()->current_render_pass->color_space);
+  } else {
+    if (render_pass->force_render_surface)

[reveman, 2017/05/10 13:06:17]

I'm not sure we can do this without also checking that render pass doesn't have
damage. We need to update the texture if it's damaged. If it's not damaged then
I think we can now return early here as it's not clipped when this flag is set.

We'll need comment here to explain this.

[wutao, 2017/05/11 19:36:34]

Tested in some animation and the render_pass->damage_rect get damaged for most
of time. Remove this early return for now. Improve late.

+      return false;
   }
   DCHECK(texture->id());