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 c858794fe836c173daa354c437ed73fef0562e7d..e32f759d83768562f7527091bc4a299fc34baacf 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/FrameView.h"
@@ -79,12 +80,15 @@ AutoscrollController* ScrollManager::GetAutoscrollController() const {
 }
 
 void ScrollManager::RecomputeScrollChain(const Node& start_node,
+                                         const ScrollState& scroll_state,
                                          std::deque<int>& scroll_chain) {
   scroll_chain.clear();
 
   DCHECK(start_node.GetLayoutObject());
   LayoutBox* cur_box = start_node.GetLayoutObject()->EnclosingBox();
   Element* document_element = frame_->GetDocument()->documentElement();
+  bool x_dominated =
+      (std::abs(scroll_state.deltaX()) > std::abs(scroll_state.deltaY()));
 
   // Scrolling propagates along the containing block chain and ends at the
   // RootScroller element. The RootScroller element will have a custom
@@ -108,6 +112,14 @@ void ScrollManager::RecomputeScrollChain(const Node& start_node,
       if (IsViewportScrollingElement(*cur_element) ||
           cur_element == document_element)
         break;
+
+      if ((x_dominated &&
+           cur_element->GetComputedStyle()->ScrollBoundaryBehaviorX() !=
+               EScrollBoundaryBehavior::kAuto) ||
+          (!x_dominated &&
+           cur_element->GetComputedStyle()->ScrollBoundaryBehaviorY() !=
+               EScrollBoundaryBehavior::kAuto))
+        break;
     }
 
     cur_box = cur_box->ContainingBlock();
@@ -188,14 +200,14 @@ void ScrollManager::CustomizedScroll(const Node& start_node,
   if (scroll_state.FullyConsumed())
     return;
 
-  if (scroll_state.deltaX() || scroll_state.deltaY())
+  if (scroll_state.deltaX() || scroll_state.deltaY()) {
     frame_->GetDocument()->UpdateStyleAndLayoutIgnorePendingStylesheets();
+    if (current_scroll_chain_.empty())
+      RecomputeScrollChain(start_node, scroll_state, current_scroll_chain_);
+    scroll_state.SetScrollChain(current_scroll_chain_);
 
-  if (current_scroll_chain_.empty())
-    RecomputeScrollChain(start_node, current_scroll_chain_);
-  scroll_state.SetScrollChain(current_scroll_chain_);
-
-  scroll_state.distributeToScrollChainDescendant();
+    scroll_state.distributeToScrollChainDescendant();
+  }
 }
 
 void ScrollManager::ComputeScrollRelatedMetrics(