Make scrollWidth and scrollHeight match other DOM measurement APIs

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index aa9c0c56bccd29c71180100aff6a108e5fb3b97e..f53f772728ff7af90ea0a4f784c329c0ed1382d5 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3375,12 +3375,15 @@ 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(); // Already accounts for zoom.
-    int heightScaled = static_cast<int>(document->documentElement()->scrollHeight() * zoomLevelToZoomFactor(zoomLevel()));
+    LayoutBox* documentBox = document->documentElement()->layoutBox();
+    // TODO(leviw): We truncate then zoom the height instead of rounding to match the width behavior. We
+    // should be able to call documentElement's scrollHeight() method. crbug.com/471336
+    int heightScaled = adjustLayoutUnitForAbsoluteZoom(documentBox->scrollHeight(), *documentBox).toInt() * zoomLevelToZoomFactor(zoomLevel());
     return IntSize(widthScaled, heightScaled);
 }