Update WebViewImpl::contentsPreferredMinimumSize to be agnostic to the scrolling element

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index 6eb50580c2bf29e160f74b222c7187075b105a8d..442a6e6fafd88ac6fb79b4bd1b392e1ac3091d6b 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3397,12 +3397,13 @@ IntSize WebViewImpl::contentsSize() const
 WebSize WebViewImpl::contentsPreferredMinimumSize()
 {
     Document* document = m_page->mainFrame()->isLocalFrame() ? m_page->deprecatedLocalMainFrame()->document() : 0;
-    if (!document || !document->layoutView() || !document->documentElement())
+    if (!document || !document->layoutView() || !document->documentElement() || !document->documentElement()->layoutBox())
         return WebSize();
 
     layout();
     int widthScaled = document->layoutView()->minPreferredLogicalWidth().round(); // Already accounts for zoom.
-    int heightScaled = static_cast<int>((document->documentElement()->scrollHeight() * zoomLevelToZoomFactor(zoomLevel())) + 0.5); // +0.5 to round rather than truncating
+    LayoutBox* box = document->documentElement()->layoutBox();
+    int heightScaled = static_cast<int>(adjustLayoutUnitForAbsoluteZoom(box->scrollHeight(), *box) * zoomLevelToZoomFactor(zoomLevel()) + 0.5); // +0.5 to round rather than truncating

[bokan, 2015/08/13 15:49:04]

Did you forget to remove the second zoom factor? It looks like we're double
applying. Also, just use .round() on the layout unit instead of the cast and '+
0.5'.

[Rick Byers, 2015/08/13 16:51:54]

I was attempting to leave the behavior exactly the same as before.  I _think_
adjustLayoutUnitForAbsoluteZoom is applying only css zoom, where
zoomLevelToZoomFactor is applying page zoom.  
The result of a LayoutUnit times a double is a double.  Of course I could use
'round' instead of this ugly addition, but the cast is still necessary.

     return IntSize(widthScaled, heightScaled);
 }