Revert of Discard compositor frames from unloaded web content

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 9a5deabf7aa8d745cfef71e8108d5d0cddbeb321..809ffb68c004c3d3ad3ac128980a0f60b52add2a 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -309,9 +309,6 @@
     return painted_device_scale_factor_;
   }
 
-  void SetContentSourceId(uint32_t);
-  uint32_t content_source_id() const { return content_source_id_; }
-
   void SetDeviceColorSpace(const gfx::ColorSpace& device_color_space);
   const gfx::ColorSpace& device_color_space() const {
     return device_color_space_;
@@ -573,8 +570,6 @@
   float max_page_scale_factor_ = 1.f;
   gfx::ColorSpace device_color_space_;
 
-  uint32_t content_source_id_;
-
   SkColor background_color_ = SK_ColorWHITE;
   bool has_transparent_background_ = false;