Store non-fast scrollable regions on ScrollNode

cc/trees/scroll_node.h

Index: cc/trees/scroll_node.h
diff --git a/cc/trees/scroll_node.h b/cc/trees/scroll_node.h
index 3e4f4e98ea2ef5bba3cb6e0f0fb7bf073f8fa603..7138f3ab5c80d235d589f8e08bd6cb7c99ba2316 100644
--- a/cc/trees/scroll_node.h
+++ b/cc/trees/scroll_node.h
@@ -6,6 +6,7 @@
 #define CC_TREES_SCROLL_NODE_H_
 
 #include "cc/base/cc_export.h"
+#include "cc/base/region.h"
 #include "cc/output/filter_operations.h"
 #include "ui/gfx/geometry/size.h"
 
@@ -37,7 +38,8 @@ struct CC_EXPORT ScrollNode {
   bool scrollable;
 
   uint32_t main_thread_scrolling_reasons;
-  bool contains_non_fast_scrollable_region;
+
+  Region non_fast_scrollable_region;

[wkorman, 2017/02/27 23:59:24]

Just to note, this replaces a per-node bool with an SkIRect and a pointer
(cc::Region has an SkRegion field, and see SkRegion::{fBounds,fRunHead}). Still
seems worthwhile for the code evolution goal.

[pdr., 2017/02/28 19:36:47]

This is a good point and I hadn't fully groked it. Do you think we should add a
comment to the code, or were you just noting this difference?

[wkorman, 2017/02/28 20:50:16]

I don't think we need a comment, I was just noting it as I was reading, to make
sure we knew about the add'l size.

 
   // Size of the clipped area, not including non-overlay scrollbars. Overlay
   // scrollbars do not affect the clipped area.