FrameView now notifies ScrollCoorinator of changes in its scrollable area set

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index b86590a19cc5de006a1f84c56aab1321de50ddea..6bde998667c9feb54e252f083aa2917cf156dba9 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -118,6 +118,15 @@ void ScrollingCoordinator::notifyLayoutUpdated()
     m_shouldScrollOnMainThreadDirty = true;
 }
 
+void ScrollingCoordinator::scrollAreaSetDidChange()
+{
+    // Wait until after layout to update.

[Ian Vollick, 2015/01/07 17:58:03]

Why don't we want to set the dirty bit when we need a layout? Will a layout
force this to be updated?

[majidvp, 2015/01/07 19:52:28]

A layout also sets the same dirty flag forcing the same update making this one
redundant. (See |ScrollingCoordinator::notifyLayoutUpdate|)
Since a layout may update these scrollable area bounding boxes, I think it makes
sense to wait for layout completion before computing the non-fast scroll
regions.

[Ian Vollick, 2015/01/07 19:56:23]

Ah, thanks, that makes sense. In that case, could you please update the comment
to reassure the future reader that everything's going to be fine after the
layout? :)

[majidvp, 2015/01/12 16:28:27]

Done.

+    if (!m_page->deprecatedLocalMainFrame()->view() || m_page->deprecatedLocalMainFrame()->view()->needsLayout())
+        return;
+
+    m_scrollGestureRegionIsDirty = true;
+}
+
 void ScrollingCoordinator::updateAfterCompositingChangeIfNeeded()
 {
     if (!m_page->mainFrame()->isLocalFrame())