Initial viewport is not the same as FrameView rect.

third_party/WebKit/Source/core/css/MediaValuesInitialViewport.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/MediaValuesInitialViewport.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/api/LayoutViewItem.h"
 
 namespace blink {
 
 MediaValues* MediaValuesInitialViewport::create(LocalFrame& frame) {
   return new MediaValuesInitialViewport(frame);
 }
 
 MediaValuesInitialViewport::MediaValuesInitialViewport(LocalFrame& frame)
     : MediaValuesDynamic(&frame) {}
 
 double MediaValuesInitialViewport::viewportWidth() const {
-  DCHECK(m_frame->view() && m_frame->document());
-  int viewportWidth = m_frame->view()->frameRect().width();
-  return adjustDoubleForAbsoluteZoom(
-      viewportWidth, m_frame->document()->layoutViewItem().styleRef());
+  DCHECK(m_frame->view());
+  return m_frame->view()->initialViewportWidth();

[bokan, 2016/10/18 17:19:26]

I'm a stranger around these parts, but m_frame can be an iframe, right? I don't
see where we set the initialViewport size for non-main frames.

[rune, 2016/10/18 22:09:53]

Right, MediaValuesInitialViewport are only used for @viewport descriptors and
@media evaluation for collecting @viewport rules.

@viewport rules are only collected for main frames. That is, they will only be
collected for main frames after [1]. Before [1] they are collected, but setting
the viewport description has no effect since we're checking for main frame
before doing anything with it.

It would be more consistent if we initialized FrameView's initialViewportSize
for non-main frames as well?

Or perhaps DCHECKs for being called from a main frame?

[1] https://codereview.chromium.org/2420413005/

[bokan, 2016/10/18 22:28:06]

Ok. I'm fine with either approach though DCHECKs for main frame are probably
better since we don't expect initialViewport to be used from iframes for now.

[rune, 2016/10/18 22:56:12]

DCHECKs added.

 }
 
 double MediaValuesInitialViewport::viewportHeight() const {
-  DCHECK(m_frame->view() && m_frame->document());
-  int viewportHeight = m_frame->view()->frameRect().height();
-  return adjustDoubleForAbsoluteZoom(
-      viewportHeight, m_frame->document()->layoutViewItem().styleRef());
+  DCHECK(m_frame->view());
+  return m_frame->view()->initialViewportHeight();
 }
 
 }  // namespace blink