cc : Fix the bug in tracking currently running animations for an element

cc/animation/element_animations.cc

Index: cc/animation/element_animations.cc
diff --git a/cc/animation/element_animations.cc b/cc/animation/element_animations.cc
index 35de36725d0732d55d31f11a50e2434867524243..32da627aa5cbbc9957830a1113137a6e10ff817f 100644
--- a/cc/animation/element_animations.cc
+++ b/cc/animation/element_animations.cc
@@ -635,11 +635,11 @@ void ElementAnimations::UpdateClientAnimationStateInternal(
             animation->affects_active_elements();
         animation_state->potentially_animating_for_pending_elements |=
             animation->affects_pending_elements();
-        animation_state->currently_running_for_active_elements =
-            animation_state->potentially_animating_for_active_elements &&
+        animation_state->currently_running_for_active_elements |=
+            animation->affects_active_elements() &&
             animation->InEffect(last_tick_time_);
-        animation_state->currently_running_for_pending_elements =
-            animation_state->potentially_animating_for_pending_elements &&
+        animation_state->currently_running_for_pending_elements |=
+            animation->affects_pending_elements() &&
             animation->InEffect(last_tick_time_);

[loyso (OOO), 2016/09/14 23:49:08]

NIT: Would be nice to add a DCHECK as a loop invariant.
Given that p = potentially_animating_for_pending_elements, c =
currently_running_for_active_elements, c must be a subset of p (c <= p).
i.e.:
// DNF: (!p && !c) || (p && !c) || (p && c)
DCHECK_LE(c, p);

In C++ you can compare the order of bool values, they are promoted to int as
false -> 0, true -> 1.

       }
     }