Fix the bug that negative outline-offset is covered up by composited

third_party/WebKit/Source/platform/graphics/CompositingReasons.h

Index: third_party/WebKit/Source/platform/graphics/CompositingReasons.h
diff --git a/third_party/WebKit/Source/platform/graphics/CompositingReasons.h b/third_party/WebKit/Source/platform/graphics/CompositingReasons.h
index 0513a7340904ea3c18e5d345c95d47a1bfab3bc3..e45fea06b57191dee26d64c5e16e11abdfb46fd4 100644
--- a/third_party/WebKit/Source/platform/graphics/CompositingReasons.h
+++ b/third_party/WebKit/Source/platform/graphics/CompositingReasons.h
@@ -93,6 +93,9 @@ const uint64_t CompositingReasonInlineTransform = UINT64_C(1) << 48;
 
 const uint64_t CompositingReasonCompositorProxy = UINT64_C(1) << 49;
 
+// Composited layer painted on top of all other layers as decoration
+const uint64_t CompositingReasonLayerForDecoration = UINT64_C(1) << 50;

[flackr, 2016/10/24 17:19:30]

We don't need to add a compositing reason for this - we should never composite
something just because it has a negative-offset outline, it will just create an
extra layer when composited if we need to for  the outline.

[yigu, 2016/10/24 20:31:36]

Will add a compositing reason as discussed.

+
 // Various combinations of compositing reasons are defined here also, for more
 // intutive and faster bitwise logic.
 const uint64_t CompositingReasonComboAllDirectReasons =