MacViews: Support continuous scrolling and horizontal scrolling

ui/views/controls/scrollbar/base_scroll_bar.cc

Index: ui/views/controls/scrollbar/base_scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/base_scroll_bar.cc b/ui/views/controls/scrollbar/base_scroll_bar.cc
index 2f07692bf8a3b32a9d18c95937dd6463daa08f31..4998582c3c3968c02509fbf714535209916bd936 100644
--- a/ui/views/controls/scrollbar/base_scroll_bar.cc
+++ b/ui/views/controls/scrollbar/base_scroll_bar.cc
@@ -194,7 +194,7 @@ bool BaseScrollBar::OnKeyPressed(const ui::KeyEvent& event) {
 }
 
 bool BaseScrollBar::OnMouseWheel(const ui::MouseWheelEvent& event) {
-  ScrollByContentsOffset(event.y_offset());
+  ScrollByContentsOffset(IsHorizontal() ? event.x_offset() : event.y_offset());

[tapted, 2014/09/02 09:10:25]

Maybe this should be doing `return OnScroll(event.x_offset(),
event.y_offset());`

[Andre, 2014/09/02 17:05:05]

Done.
But I kept the return true because OnScroll can return false, which might cause
unwanted behavior
change in case of nested scroll views.

   return true;
 }