Add EventHandlerRegistry

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 c09c01c5755f87eab0487d5af1a31e37ae6fe59b..07afe72fd5b3124449dd5f9b760aef4bce043b79 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -29,8 +29,8 @@
 
 #include "RuntimeEnabledFeatures.h"
 #include "core/dom/Document.h"
+#include "core/dom/EventHandlerRegistry.h"
 #include "core/dom/Node.h"
-#include "core/dom/WheelController.h"
 #include "core/html/HTMLElement.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ -623,11 +623,22 @@ void ScrollingCoordinator::setWheelEventHandlerCount(unsigned count)
         scrollLayer->setHaveWheelEventHandlers(count > 0);
 }
 
+void ScrollingCoordinator::setScrollEventHandlerCount(unsigned count)
+{
+    if (WebLayer* scrollLayer = toWebLayer(m_page->mainFrame()->view()->layerForScrolling()))
+        scrollLayer->setHaveScrollEventHandlers(count > 0);
+}
+
 void ScrollingCoordinator::recomputeWheelEventHandlerCountForFrameView(FrameView*)
 {
     setWheelEventHandlerCount(computeCurrentWheelEventHandlerCount());
 }
 
+void ScrollingCoordinator::recomputeScrollEventHandlerCountForFrameView(FrameView*)

[Rick Byers, 2014/03/24 14:27:59]

What you're doing here seems conceptually similar to the code in
Document::didAdd/Remove/ClearTouchEventHandler that calls
frameHost->chrome().client().needTouchEvents(true/false) whenever we transition
between no handlers and some handlers.  Can we generalize that somehow?

One option is having the EventHandlerRegistry chain between documents the way
the touch handler stuff does today (so any number of handlers in a child
document count as one handler in the parent) and then expose an API for when it
changes.

Alternately, if it's simpler I'm not opposed to walking the frame tree to
compute this when needed (should always be cheap), but then we should probably
do the same for the touch handlers.

One thing you may want to think about is the impact on out-of-process iframes /
site-isolation.  I haven't figured out yet how the touch handler tracking needs
to change for site-isolation, but if you're refactoring all this then it
probably makes sense to have some idea for how it'll eventually handle site
isolation.  I'm guessing having an outside process compute the document-wide
view will fit much better with the site-isolation model.

+{
+    setScrollEventHandlerCount(computeCurrentScrollEventHandlerCount());
+}
+
 void ScrollingCoordinator::setShouldUpdateScrollLayerPositionOnMainThread(MainThreadScrollingReasons reasons)
 {
     if (WebLayer* scrollLayer = toWebLayer(m_page->mainFrame()->view()->layerForScrolling())) {
@@ -791,12 +802,24 @@ unsigned ScrollingCoordinator::computeCurrentWheelEventHandlerCount()
 
     for (LocalFrame* frame = m_page->mainFrame(); frame; frame = frame->tree().traverseNext()) {
         if (frame->document())
-            wheelEventHandlerCount += WheelController::from(*frame->document())->wheelEventHandlerCount();
+            wheelEventHandlerCount += EventHandlerRegistry::from(*frame->document())->wheelEventHandlerCount();
     }
 
     return wheelEventHandlerCount;
 }
 
+unsigned ScrollingCoordinator::computeCurrentScrollEventHandlerCount()
+{
+    unsigned scrollEventHandlerCount = 0;
+
+    for (LocalFrame* frame = m_page->mainFrame(); frame; frame = frame->tree().traverseNext()) {
+        if (frame->document())
+            scrollEventHandlerCount += EventHandlerRegistry::from(*frame->document())->scrollEventHandlerCount();
+    }
+
+    return scrollEventHandlerCount;
+}
+
 void ScrollingCoordinator::frameViewWheelEventHandlerCountChanged(FrameView* frameView)
 {
     ASSERT(isMainThread());
@@ -805,6 +828,14 @@ void ScrollingCoordinator::frameViewWheelEventHandlerCountChanged(FrameView* fra
     recomputeWheelEventHandlerCountForFrameView(frameView);
 }
 
+void ScrollingCoordinator::frameViewScrollEventHandlerCountChanged(FrameView* frameView)
+{
+    ASSERT(isMainThread());
+    ASSERT(m_page);
+
+    recomputeScrollEventHandlerCountForFrameView(frameView);
+}
+
 void ScrollingCoordinator::frameViewHasSlowRepaintObjectsDidChange(FrameView* frameView)
 {
     ASSERT(isMainThread());
@@ -855,6 +886,7 @@ void ScrollingCoordinator::frameViewRootLayerDidChange(FrameView* frameView)
 
     notifyLayoutUpdated();
     recomputeWheelEventHandlerCountForFrameView(frameView);
+    recomputeScrollEventHandlerCountForFrameView(frameView);
 }
 
 #if OS(MACOSX)