Use scroll customization primitives for touch scrolling (behind REF).

Source/core/frame/LocalFrame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 747 matching lines @@
 bool LocalFrame::shouldReuseDefaultView(const KURL& url) const
 {
     return loader().stateMachine()->isDisplayingInitialEmptyDocument() && document()->isSecureTransitionTo(url);
 }
 
 void LocalFrame::removeSpellingMarkersUnderWords(const Vector<String>& words)
 {
     spellChecker().removeSpellingMarkersUnderWords(words);
 }
 
+static bool scrollAreaOnBothAxes(const FloatSize& delta, ScrollableArea& view)
+{
+    bool scrolledHorizontal = view.scroll(ScrollLeft, ScrollByPrecisePixel, delta.width());
+    bool scrolledVertical = view.scroll(ScrollUp, ScrollByPrecisePixel, delta.height());
+    return scrolledHorizontal || scrolledVertical;

[Rick Byers, 2015/03/11 02:22:18]

again, don't you need to handle these two cases separately?  Eg. what about a
vertically scrollable iframe nested inside of a horizontally scrollable
document?

perhaps 'bool LocalFrame::applyScrollDelta' should just be 'void
LocalFrame::applyScroll(ScrollState&)'?

Ah, I see - this function is used in both custom and standard scroll cases. 
Maybe just mention that in a comment, with a FIXME if you think you can simplify
it once scroll customization is enabled by default.

[tdresser, 2015/03/20 18:00:36]

This doesn't change any behavior, see 
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit....

Main thread scroll bubbling across iframes doesn't feel great.
I'll add a test for diagonal scrolling across iframes at the same time as I fix
it (crbug.com/466991).

I did have a version of this patch which passed a ScrollState here, and it was
quite pretty, especially the top controls part. For now, I've added the FIXME,
because that change does make it a pain to get the non-scroll customized world
working.

[Rick Byers, 2015/03/26 21:22:49]

Ok, SGTM - thanks.

+}
+
+// Returns true if a scroll occurred.
+bool LocalFrame::applyScrollDelta(const FloatSize& delta, bool isScrollBegin)
+{
+    if (isScrollBegin)
+        host()->topControls().scrollBegin();
+
+    if (!view() || delta.isZero())
+        return false;
+
+    FloatSize remainingDelta = delta;
+
+    // If this is main frame, allow top controls to scroll first and update
+    // |remainingDelta| accordingly
+    bool giveToTopControls = false;
+    if (isMainFrame()) {
+        // Always give the delta to the top controls if the scroll is in
+        // the direction to show the top controls. If it's in the
+        // direction to hide the top controls, only give the delta to the
+        // top controls when the frame can scroll.
+        giveToTopControls = remainingDelta.height() > 0
+            || view()->scrollPosition().y() < view()->maximumScrollPosition().y();
+    }
+
+    if (giveToTopControls)
+        remainingDelta = host()->topControls().scrollBy(remainingDelta);
+
+    if (remainingDelta.isZero())
+        return true;
+
+    if (scrollAreaOnBothAxes(remainingDelta, *view()))
+        return true;
+
+    // If this is the main frame and it didn't scroll, propagate up to the pinch viewport.
+    if (!settings()->pinchVirtualViewportEnabled() || !isMainFrame())
+        return false;
+
+    if (scrollAreaOnBothAxes(remainingDelta, page()->frameHost().pinchViewport()))
+        return true;
+
+    return false;
+}
+
 #if ENABLE(OILPAN)
 void LocalFrame::registerPluginElement(HTMLPlugInElement* plugin)
 {
     m_pluginElements.add(plugin);
 }
 
 void LocalFrame::unregisterPluginElement(HTMLPlugInElement* plugin)
 {
     ASSERT(m_pluginElements.contains(plugin));
     m_pluginElements.remove(plugin);
@@ skipping 46 matching lines @@
     // We detach the FrameView's custom scroll bars as early as
     // possible to prevent m_doc->detach() from messing with the view
     // such that its scroll bars won't be torn down.
     //
     // FIXME: We should revisit this.
     if (m_view)
         m_view->prepareForDetach();
 }
 
 } // namespace blink