vh units shouldn't add controls height when controls are locked to hidden.

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

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1382 matching lines @@
 
     us.intersect(parentRect);
   }
 
   return us;
 }
 
 FloatSize FrameView::viewportSizeForViewportUnits() const {
   float zoom = frame().pageZoomFactor();
 
-  FloatSize layoutSize;
-
   LayoutViewItem layoutViewItem = this->layoutViewItem();
   if (layoutViewItem.isNull())
-    return layoutSize;
+    return FloatSize();
 
+  FloatSize layoutSize;
   layoutSize.setWidth(layoutViewItem.viewWidth(IncludeScrollbars) / zoom);
   layoutSize.setHeight(layoutViewItem.viewHeight(IncludeScrollbars) / zoom);
 
-  if (RuntimeEnabledFeatures::inertTopControlsEnabled()) {
+  BrowserControls& browserControls = m_frame->host()->browserControls();
+  if (RuntimeEnabledFeatures::inertTopControlsEnabled() &&
+      browserControls.permittedState() != WebBrowserControlsHidden) {
     // We use the layoutSize rather than frameRect to calculate viewport units
     // so that we get correct results on mobile where the page is laid out into
     // a rect that may be larger than the viewport (e.g. the 980px fallback
     // width for desktop pages). Since the layout height is statically set to
     // be the viewport with browser controls showing, we add the browser
     // controls height, compensating for page scale as well, since we want to
     // use the viewport with browser controls hidden for vh (to match Safari).
-    BrowserControls& browserControls = m_frame->host()->browserControls();
     int viewportWidth = m_frame->host()->visualViewport().size().width();
     if (m_frame->isMainFrame() && layoutSize.width() && viewportWidth) {
       float pageScaleAtLayoutWidth = viewportWidth / layoutSize.width();
       layoutSize.expand(0, browserControls.height() / pageScaleAtLayoutWidth);
     }
   }
 
   return layoutSize;
 }
 
@@ skipping 3772 matching lines @@
 void FrameView::setAnimationHost(
     std::unique_ptr<CompositorAnimationHost> host) {
   m_animationHost = std::move(host);
 }
 
 LayoutUnit FrameView::caretWidth() const {
   return LayoutUnit(getHostWindow()->windowToViewportScalar(1));
 }
 
 }  // namespace blink