Implement CSS: scroll-boundary-behavior

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index afd92778924c0f381ab4be208aa702b9a4622bf4..a5a91353ff317ef7dd1b90e841ed5250dbd71bc0 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -81,6 +81,7 @@
 #include "platform/wtf/CurrentTime.h"
 #include "platform/wtf/text/StringBuilder.h"
 #include "public/platform/WebLayerStickyPositionConstraint.h"
+#include "public/platform/WebScrollBoundaryBehavior.h"
 
 namespace blink {
 
@@ -1139,11 +1140,27 @@ void CompositedLayerMapping::UpdateGraphicsLayerGeometry(
   UpdateShouldFlattenTransform();
   UpdateChildrenTransform();
   UpdateScrollParent(ScrollParent());
+  UpdateScrollBoundaryBehavior();
   RegisterScrollingLayers();
 
   UpdateCompositingReasons();
 }
 
+void CompositedLayerMapping::UpdateScrollBoundaryBehavior() {
+  EScrollBoundaryBehavior behavior_x =
+      GetLayoutObject().StyleRef().ScrollBoundaryBehaviorX();
+  EScrollBoundaryBehavior behavior_y =
+      GetLayoutObject().StyleRef().ScrollBoundaryBehaviorY();
+  if (scrolling_contents_layer_) {
+    using ScrollBoundaryBehavior =
+        WebScrollBoundaryBehavior::ScrollBoundaryBehaviorType;

[majidvp, 2017/07/05 21:30:03]

nit: I don't feel like this using declaration is helping much with
the readability of this code. It is just saving typing
'WebScrollBoundaryBehavior' twice below. Also the naming is confusing
as it removes the Type prefix. I suggest not having it and just specifying the
exact type below.

[sunyunjia, 2017/07/14 02:59:01]

Done.

+    scrolling_contents_layer_->SetScrollBoundaryBehavior(
+        WebScrollBoundaryBehavior(
+            static_cast<ScrollBoundaryBehavior>(behavior_x),
+            static_cast<ScrollBoundaryBehavior>(behavior_y)));
+  }
+}
+
 void CompositedLayerMapping::UpdateMainGraphicsLayerGeometry(
     const IntRect& relative_compositing_bounds,
     const IntRect& local_compositing_bounds,