Don't set shownRatio in main thread top controls on animated state change.

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

 // Copyright 2015 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/frame/TopControls.h"
 
 #include "core/frame/FrameHost.h"
 #include "core/frame/VisualViewport.h"
 #include "core/page/ChromeClient.h"
 #include "platform/geometry/FloatSize.h"
@@ skipping 77 matching lines @@
     shownRatio = std::min(shownRatio, 1.f);
     shownRatio = std::max(shownRatio, 0.f);
 
     if (m_shownRatio == shownRatio)
         return;
 
     m_shownRatio = shownRatio;
     m_frameHost->chromeClient().didUpdateTopControls();
 }
 
-void TopControls::updateConstraints(WebTopControlsState constraints)
+void TopControls::updateConstraintsAndState(
+    WebTopControlsState constraints,
+    WebTopControlsState current,
+    bool animate)
 {
     m_permittedState = constraints;
 
-    if (m_permittedState == WebTopControlsShown)
-        setShownRatio(1.f);
-    else if (m_permittedState == WebTopControlsHidden)
-        setShownRatio(0.f);
+    // If the change should be animated, let the impl thread drive the change.
+    // Otherwise, immediately set the shown ratio so we don't have to wait for
+    // a commit from the impl thread.
+    if (!animate) {
+        switch (current) {

[majidvp, 2016/06/29 13:56:09]

Sorry to go back and forth and not noticing this earlier but this should
actually be |constraints| not the |current|. In fact, |current| is always |Both|
which makes it a no-op.

In CC we make the decision based on both and assert that they cannot be
contradictory. Perhaps we should just replicate the same logic here and not
assume current is always BOTH.

[bokan, 2016/06/29 16:23:00]

Good catch, I hadn't noticed this doesn't fix the race it was meant for since it
apparently doesn't occur in Debug builds. I've fixed this to mirror CC more
closely.

+        case WebTopControlsShown:
+            setShownRatio(1.f);
+            break;
+        case WebTopControlsHidden:
+            setShownRatio(0.f);
+            break;
+        case WebTopControlsBoth:
+        default:
+            break;
+        }
+    }
 }
 
 void TopControls::setHeight(float height, bool shrinkViewport)
 {
     if (m_height == height && m_shrinkViewport == shrinkViewport)
         return;
 
     m_height = height;
     m_shrinkViewport = shrinkViewport;
     m_frameHost->chromeClient().didUpdateTopControls();
 }
 
 } // namespace blink