Refactor viewport initialization logic out of WebViewImpl.

Source/core/page/Page.cpp

Index: Source/core/page/Page.cpp
diff --git a/Source/core/page/Page.cpp b/Source/core/page/Page.cpp
index 6c7942b237f980b442317913cffe51b832aaa08b..dcbef4dd45ba52b2d87d520bd3ee48622a253560 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -447,24 +447,25 @@ 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);
 
-    m_pageScaleFactor = scale;
+    if (scale != m_pageScaleFactor) {
+        m_pageScaleFactor = scale;
 
-    if (view)
-        view->setVisibleContentScaleFactor(scale);
+        if (view)
+            view->setVisibleContentScaleFactor(scale);
 
-    mainFrame()->deviceOrPageScaleFactorChanged();
+        mainFrame()->deviceOrPageScaleFactorChanged();
 
-    if (view)
-        view->setViewportConstrainedObjectsNeedLayout();
+        if (view)
+            view->setViewportConstrainedObjectsNeedLayout();
+    }
 
     if (view && view->scrollPosition() != origin)
-        view->setScrollPosition(origin);
+        view->notifyScrollPositionChanged(origin);
+
+    view->setInProgrammaticScroll(oldProgrammaticScroll);
 }
 
 void Page::setDeviceScaleFactor(float scaleFactor)