Implement CSS: scroll-boundary-behavior

third_party/WebKit/Source/core/input/ScrollManager.cpp

Index: third_party/WebKit/Source/core/input/ScrollManager.cpp
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.cpp b/third_party/WebKit/Source/core/input/ScrollManager.cpp
index 0d4a7cb180e276e187db3c6488917ace6589fea7..3b6b4d17f7d69f53eeabe430f7ba4687fb50fa6e 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -6,6 +6,7 @@
 
 #include <memory>
 #include "core/dom/DOMNodeIds.h"
+#include "core/dom/NodeComputedStyle.h"
 #include "core/events/GestureEvent.h"
 #include "core/frame/BrowserControls.h"
 #include "core/frame/LocalFrameView.h"
@@ -117,6 +118,9 @@ void ScrollManager::RecomputeScrollChain(const Node& start_node,
       if (IsViewportScrollingElement(*cur_element) ||
           cur_element == document_element)
         break;
+
+      if (!CanPropagate(scroll_state, *cur_element))
+        break;
     }
 
     cur_box = cur_box->ContainingBlock();
@@ -152,6 +156,22 @@ bool ScrollManager::CanScroll(const ScrollState& scroll_state,
   return clamped_offset != current_offset;
 }
 
+bool ScrollManager::CanPropagate(const ScrollState& scroll_state,
+                                 const Element& current_element) {

[majidvp, 2017/07/14 14:29:44]

ditto. This function does not need to be a member function.

nit: The name |current_element| is not very appropriate here.
There is no other element so just calling it scrolling_element
or just element is better IMHO. 

[sunyunjia, 2017/07/14 22:07:24]

Done.

+  // ScrollBoundaryBehavior may have different values on x-axis and y-axis.
+  // We need to find out the dominant axis of user's intended scroll to decide
+  // which ScrollBoundaryBehavior should be applied, i.e. which node should
+  // be scrolled.

[majidvp, 2017/07/14 14:29:44]

ditto. the last sentence of the comment is not accurate.

[sunyunjia, 2017/07/14 22:07:24]

Done.

+  bool x_dominant =
+      std::abs(scroll_state.deltaXHint()) > std::abs(scroll_state.deltaYHint());
+  return (x_dominant &&
+          current_element.GetComputedStyle()->ScrollBoundaryBehaviorX() ==
+              EScrollBoundaryBehavior::kAuto) ||
+         (!x_dominant &&
+          current_element.GetComputedStyle()->ScrollBoundaryBehaviorY() ==
+              EScrollBoundaryBehavior::kAuto);
+}
+
 bool ScrollManager::LogicalScroll(ScrollDirection direction,
                                   ScrollGranularity granularity,
                                   Node* start_node,