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();
+    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)