(Reland) Always create top controls manager

cc/input/top_controls_manager.cc

Index: cc/input/top_controls_manager.cc
diff --git a/cc/input/top_controls_manager.cc b/cc/input/top_controls_manager.cc
index 7362805de99acba4c5caa3145f9f268df1778336..bf0bf3fe4a05087f67c1e4fa2397abb6e04c5166 100644
--- a/cc/input/top_controls_manager.cc
+++ b/cc/input/top_controls_manager.cc
@@ -69,6 +69,9 @@ float TopControlsManager::TopControlsHeight() const {
 void TopControlsManager::UpdateTopControlsState(TopControlsState constraints,
                                                 TopControlsState current,
                                                 bool animate) {
+  if (!TopControlsEnabled())

[aelias_OOO_until_Jul13, 2015/03/04 20:05:53]

This one shouldn't be suppressed by height.  We should still be respecting the
state update even at height 0 (so the ratio is correct if the height changes
later).

[bokan, 2015/03/04 21:48:30]

Done.

+    return;
+
   DCHECK(!(constraints == SHOWN && current == HIDDEN));
   DCHECK(!(constraints == HIDDEN && current == SHOWN));
 
@@ -94,6 +97,9 @@ void TopControlsManager::UpdateTopControlsState(TopControlsState constraints,
 }
 
 void TopControlsManager::ScrollBegin() {
+  if (!TopControlsEnabled())

[aelias_OOO_until_Jul13, 2015/03/04 20:05:53]

I think we should remove all of the extra early-returns you added outside of
ScrollBy.  In particular, if the height ever changes to nonzero when a scroll
already is in progress, that will work better if we run as much of the usual
logic as possible.

[bokan, 2015/03/04 21:48:30]

Done.

+    return;
+
   DCHECK(!pinch_gesture_active_);
   ResetAnimations();
   ResetBaseline();
@@ -101,6 +107,9 @@ void TopControlsManager::ScrollBegin() {
 
 gfx::Vector2dF TopControlsManager::ScrollBy(
     const gfx::Vector2dF& pending_delta) {
+  if (!TopControlsEnabled())
+    return pending_delta;
+
   if (pinch_gesture_active_)
     return pending_delta;
 
@@ -128,17 +137,26 @@ gfx::Vector2dF TopControlsManager::ScrollBy(
 }
 
 void TopControlsManager::ScrollEnd() {
+  if (!TopControlsEnabled())
+    return;
+
   DCHECK(!pinch_gesture_active_);
   StartAnimationIfNecessary();
 }
 
 void TopControlsManager::PinchBegin() {
+  if (!TopControlsEnabled())
+    return;
+
   DCHECK(!pinch_gesture_active_);
   pinch_gesture_active_ = true;
   StartAnimationIfNecessary();
 }
 
 void TopControlsManager::PinchEnd() {
+  if (!TopControlsEnabled())
+    return;
+
   DCHECK(pinch_gesture_active_);
   // Pinch{Begin,End} will always occur within the scope of Scroll{Begin,End},
   // so return to a state expected by the remaining scroll sequence.
@@ -147,10 +165,15 @@ void TopControlsManager::PinchEnd() {
 }
 
 void TopControlsManager::MainThreadHasStoppedFlinging() {
+  if (!TopControlsEnabled())
+    return;
+
   StartAnimationIfNecessary();
 }
 
 gfx::Vector2dF TopControlsManager::Animate(base::TimeTicks monotonic_time) {
+  DCHECK(TopControlsEnabled());

[aelias_OOO_until_Jul13, 2015/03/04 20:05:53]

I'd suggest removing this DCHECK.  If you're worried about unnecessary animation
frames (although I don't think it would happen in practice), you could change
SetupAnimation just set the ratio to 0/1 without animating if height is 0, and
also have a unit test if you do that.

[bokan, 2015/03/04 21:48:30]

Done.

+
   if (!top_controls_animation_ || !client_->HaveRootScrollLayer())
     return gfx::Vector2dF();
 
@@ -231,4 +254,8 @@ void TopControlsManager::ResetBaseline() {
   baseline_content_offset_ = ContentTopOffset();
 }
 
+bool TopControlsManager::TopControlsEnabled() {

[aelias_OOO_until_Jul13, 2015/03/04 20:05:53]

I don't think we should have a method called this, it's not a mode anymore.

[bokan, 2015/03/04 21:48:30]

Done.

+  return TopControlsHeight();
+}
+
 }  // namespace cc