Don't change layout size due to top control show/hide

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 22 matching lines @@
 #include "core/dom/AXObjectCache.h"
 #include "core/dom/Fullscreen.h"
 #include "core/dom/IntersectionObserverController.h"
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/RenderedPosition.h"
 #include "core/editing/markers/DocumentMarkerController.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/LocalFrame.h"
+#include "core/frame/PageScaleConstraintsSet.h"
 #include "core/frame/Settings.h"
+#include "core/frame/TopControls.h"
 #include "core/html/HTMLFrameElement.h"
 #include "core/html/HTMLPlugInElement.h"
 #include "core/html/HTMLTextFormControlElement.h"
 #include "core/html/parser/TextResourceDecoder.h"
 #include "core/input/EventHandler.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/inspector/InspectorTraceEvents.h"
 #include "core/layout/LayoutAnalyzer.h"
 #include "core/layout/LayoutCounter.h"
 #include "core/layout/LayoutEmbeddedObject.h"
@@ skipping 1051 matching lines @@
         IntRect parentRect = parent->computeVisibleArea();
         if (parentRect.isEmpty())
             return IntRect();
 
         us.intersect(parentRect);
     }
 
     return us;
 }
 
+FloatSize FrameView::viewportSizeForViewportUnits() const
+{
+    FloatSize size(layoutSize(IncludeScrollbars));
+
+    // 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 top controls showing, we add the top controls
+    // height, compensating for page scale as well, since we want to use the
+    // viewport with top controls hidden for vh (to match Safari).
+    TopControls& topControls = m_frame->host()->topControls();
+    if (m_frame->isMainFrame()) {
+        float pageScale = m_frame->host()->pageScaleConstraintsSet().finalConstraints().minimumScale;

[aelias_OOO_until_Jul13, 2016/01/16 04:17:38]

This is because of how minimum-scale is also used in mainFrameSize, I assume?

The impact of scale on this stuff is a bit subtle, could you write a unit test
checking geometry sizes in the presence of an unusual min-scale?

[bokan, 2016/01/19 00:05:31]

We say 100vh is the viewport size when top controls are hidden. When the page is
pinch-zoomable we have to also choose the scale at which we want 100vh to fill
the viewport (and use that to scale the top controls addition). I've actually
made a change here and use the scale at which viewport width == layout width. In
the common case, this will be the minimum scale. The difference is that I think
this behaves more sanely if the user specifies an explicit minimum-scale or has
a spurious "extra-wide" element on the page that implicitly increases the
minimum scale.
Done, added two for scaled page and for a minimum-scale that's smaller than the
layout width scale.

[aelias_OOO_until_Jul13, 2016/01/19 20:26:32]

Sounds good, I was going to suggest the same thing.

+        size.expand(0, topControls.height() / pageScale);
+    }
+
+    float scale = frame().pageZoomFactor();
+    size.scale(1 / scale);
+    return size;
+}
+
 DocumentLifecycle& FrameView::lifecycle() const
 {
     return m_frame->document()->lifecycle();
 }
 
 LayoutBox* FrameView::embeddedContentBox() const
 {
     LayoutView* layoutView = this->layoutView();
     if (!layoutView)
         return nullptr;
@@ skipping 2907 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink