1 files changed, 19 insertions, 5 deletions

diff --git a/chromium/ui/gfx/animation/animation_container.h b/chromium/ui/gfx/animation/animation_container.h
index a19c0539d2f..58ad1ea1d01 100644
--- a/chromium/ui/gfx/animation/animation_container.h
+++ b/chromium/ui/gfx/animation/animation_container.h
@@ -5,8 +5,9 @@
 #ifndef UI_GFX_ANIMATION_ANIMATION_CONTAINER_H_
 #define UI_GFX_ANIMATION_ANIMATION_CONTAINER_H_
 
-#include <set>
+#include <utility>
 
+#include "base/containers/flat_set.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
@@ -55,7 +56,13 @@ class ANIMATION_EXPORT AnimationContainer
  private:
   friend class base::RefCounted<AnimationContainer>;
 
-  typedef std::set<AnimationContainerElement*> Elements;
+  // This set is usually quite small so a flat_set is the most obvious choice.
+  // However, in extreme cases this can grow to 100s or even 1000s of elements.
+  // Since this set is duplicated on every call to 'Run' and indexed very
+  // frequently the cache locality of the vector is more important than the
+  // costlier (but rarer) insertion. Profiling shows that flat_set continues to
+  // perform best in these cases (up to 12x faster than std::set).
+  typedef base::flat_set<AnimationContainerElement*> Elements;
 
   ~AnimationContainer();
 
@@ -65,8 +72,9 @@ class ANIMATION_EXPORT AnimationContainer
   // Sets min_timer_interval_ and restarts the timer.
   void SetMinTimerInterval(base::TimeDelta delta);
 
-  // Returns the min timer interval of all the timers.
-  base::TimeDelta GetMinInterval();
+  // Returns the min timer interval of all the timers, and the count of timers
+  // at that interval.
+  std::pair<base::TimeDelta, size_t> GetMinIntervalAndCount() const;
 
   // Represents one of two possible values:
   // . If only a single animation has been started and the timer hasn't yet
@@ -77,8 +85,14 @@ class ANIMATION_EXPORT AnimationContainer
   // Set of elements (animations) being managed.
   Elements elements_;
 
-  // Minimum interval the timers run at.
+  // Minimum interval the timers run at, plus the number of timers that have
+  // been seen at that interval. The most common case is for all of the
+  // animations to run at 60Hz, in which case all of the intervals are the same.
+  // This acts as a cache of size 1, and when an animation stops and is removed
+  // it means that the linear scan for the new minimum timer can almost always
+  // be avoided.
   base::TimeDelta min_timer_interval_;
+  size_t min_timer_interval_count_;
 
   base::RepeatingTimer timer_;