cc: Make visible rect computation aware of pixel-moving filters

cc/trees/clip_node.h

Index: cc/trees/clip_node.h
diff --git a/cc/trees/clip_node.h b/cc/trees/clip_node.h
index fe315d460528f20b3e10a66d55842edbe5dffe93..81cf806333216ce212cd7680acc6fbe8b41c5700 100644
--- a/cc/trees/clip_node.h
+++ b/cc/trees/clip_node.h
@@ -6,6 +6,7 @@
 #define CC_TREES_CLIP_NODE_H_
 
 #include "cc/base/cc_export.h"
+#include "cc/trees/clip_expander.h"
 #include "ui/gfx/geometry/rect_f.h"
 
 namespace base {
@@ -34,7 +35,15 @@ struct CC_EXPORT ClipNode {
     NONE,
 
     // The node contributes a new clip (that is, |clip| needs to be applied).
-    APPLIES_LOCAL_CLIP
+    APPLIES_LOCAL_CLIP,
+
+    // This node represents a space expansion. When computing visible rects,
+    // the accumulated clip inherited by this node gets expanded. Similarly,
+    // when mapping a rect in descendant space to the rect in ancestor space
+    // that depends on the descendant rect's contents, this node expands the
+    // descendant rect. This is used for effects like pixel-moving filters,
+    // where clipped-out content can affect visible output.
+    EXPANDS_CLIP
   };
 
   ClipType clip_type;
@@ -43,6 +52,9 @@ struct CC_EXPORT ClipNode {
   // transform node.
   gfx::RectF clip;
 
+  // For nodes that expand, this represents the amount of expansion.
+  ClipExpander clip_expander;

[weiliangc, 2016/10/26 16:57:03]

Why not a nullable unique_ptr? We could avoid default constructor and NONE type
for the clip expander. And to transfer through protobuf we could only transfer
the effect tree id and create it on the other side?

[ajuma, 2016/10/31 17:43:07]

Done. Also added the protobuf transfer logic and a test.

+
   // Clip nodes are used for two reasons. First, they are used for determining
   // which parts of each layer are visible. Second, they are used for
   // determining whether a clip needs to be applied when drawing a layer, and if