Refactor viewport initialization logic out of WebViewImpl.

Source/core/page/Page.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All Rights Reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 429 matching lines @@
 
     m_defersLoading = defers;
     for (Frame* frame = mainFrame(); frame; frame = frame->tree()->traverseNext())
         frame->loader()->setDefersLoading(defers);
 }
 
 void Page::setPageScaleFactor(float scale, const IntPoint& origin)
 {
     FrameView* view = mainFrame()->view();
 
-    if (scale == m_pageScaleFactor) {
-        if (view && view->scrollPosition() != origin)
-            view->setScrollPosition(origin);
-        return;
+    bool oldProgrammaticScroll = view->inProgrammaticScroll();

[dshwang, 2013/05/13 12:38:01]

It is so confusing.
How about extracting scroll something from this method?

After that, if WebViewImpl want to both scale and scroll, we must call both this
method and scrolling method.

[aelias_OOO_until_Jul13, 2013/05/13 18:13:06]

The reason is that changing page scale may have the side effect of clamping the
scroll position anyway.  So if someone wants to change both scale and scroll,
they may hit the side effects of changing scroll twice.

+    view->setInProgrammaticScroll(false);
+
+    if (scale != m_pageScaleFactor) {
+        m_pageScaleFactor = scale;
+
+        if (view)
+            view->setVisibleContentScaleFactor(scale);
+
+        mainFrame()->deviceOrPageScaleFactorChanged();
+
+        if (view)
+            view->setViewportConstrainedObjectsNeedLayout();
     }
 
-    m_pageScaleFactor = scale;
+    if (view && view->scrollPosition() != origin)
+        view->notifyScrollPositionChanged(origin);
 
-    if (view)
-        view->setVisibleContentScaleFactor(scale);
-
-    mainFrame()->deviceOrPageScaleFactorChanged();
-
-    if (view)
-        view->setViewportConstrainedObjectsNeedLayout();
-
-    if (view && view->scrollPosition() != origin)
-        view->setScrollPosition(origin);
+    view->setInProgrammaticScroll(oldProgrammaticScroll);
 }
 
 void Page::setDeviceScaleFactor(float scaleFactor)
 {
     if (m_deviceScaleFactor == scaleFactor)
         return;
 
     m_deviceScaleFactor = scaleFactor;
     setNeedsRecalcStyleInAllFrames();
 
@@ skipping 350 matching lines @@
     , inspectorClient(0)
     , plugInClient(0)
 {
 }
 
 Page::PageClients::~PageClients()
 {
 }
 
 } // namespace WebCore