Hide location bar on WebKit programmatic scroll.

cc/top_controls_manager.cc

 // Copyright 2013 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 "cc/top_controls_manager.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/time.h"
@@ skipping 40 matching lines @@
       top_controls_show_height_(
           top_controls_height * top_controls_hide_threshold),
       top_controls_hide_height_(
           top_controls_height * (1.f - top_controls_show_threshold)) {
   CHECK(client_);
 }
 
 TopControlsManager::~TopControlsManager() {
 }
 
+void TopControlsManager::HideTopControls() {
+    if (controls_top_offset_ == -top_controls_height_)
+        return;
+
+    // We're in a user scroll.

[jamesr, 2013/03/04 21:44:03]

This seems kind of iffy - who's responsible for deciding if the top controls
hide or not?  Is it cc:: or the embedder (i.e. content) or WebKit or what?  I
think we need to decide on what the source of truth is and not second-guess it.

[John Knottenbelt, 2013/03/05 16:41:48]

The ultimate authority on whether the top controls should be showing is the java
FullscreenManager in the browser process. 

When the user scrolls, the TopControlsManager in cc is updating 
controls_top_offset_ and content_top_offset_. These values are plumbed through
to the browser process java FullscreenManager where they are used to translate
the top controls view (omnibox) and the content view. These values may be
overridden by the FullscreenManager under certain circumstances, for example,
the top controls will stay on screen while the page is loading, regardless of
whether the user is scrolling.

The question that the if statement is trying to address is, "what should happen
to the top controls if the user is scrolling at the same time as WebKit?" It
seems that the scroll that happened last will determine the content scrollY, so
I think, for consistency, it should also determine the position of the top
controls. This means that the if statement (line 66, 67) should be removed.

On 2013/03/04 21:44:03, jamesr wrote:

[jamesr, 2013/03/14 19:38:34]

Yeah, I think this if should be removed.

+    if (in_scroll_gesture_)
+        return;
+
+    SetupAnimation(HIDING_CONTROLS);
+}
+
 void TopControlsManager::ScrollBegin() {
   ResetAnimations();
   in_scroll_gesture_ = true;
   scroll_start_offset_ = RootScrollLayerTotalScrollY() + controls_top_offset_;
   current_scroll_delta_ = 0.f;
 }
 
 gfx::Vector2dF TopControlsManager::ScrollBy(
     const gfx::Vector2dF pending_delta) {
   if (pending_delta.y() == 0 || !enable_hiding_)
@@ skipping 142 matching lines @@
 
   if ((animation_direction_ == SHOWING_CONTROLS && new_offset >= 0) ||
       (animation_direction_ == HIDING_CONTROLS
           && new_offset <= -top_controls_height_)) {
     return true;
   }
   return false;
 }
 
 }  // namespace cc