Initial viewport is not the same as FrameView rect.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index c1d058d3ad7f28cfc677ed799b0c5128e726c3e1..0f744675dd5e47fed412d8fa6155ce5a80e574cc 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4480,4 +4480,16 @@ bool FrameView::canThrottleRendering() const {
          (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
+void FrameView::setInitialViewportSize(const IntSize& viewportSize) {
+  if (viewportSize == m_initialViewportSize)
+    return;
+
+  m_initialViewportSize = viewportSize;
+  // TODO(rune@opera.com): Notify the viewport style resolver about the changed
+  // initial viewport:
+  //
+  // if (Document* document = m_frame->document())
+  //   document->styleEngine().initialViewportChanged();
+}
+
 }  // namespace blink