Do not use NSAnimation to drive scrollbar animations.

Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 11 matching lines @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 
 #include "platform/mac/ScrollAnimatorMac.h"
 
 #include "platform/PlatformGestureEvent.h"
 #include "platform/PlatformWheelEvent.h"
+#include "platform/Timer.h"
+#include "platform/animation/TimingFunction.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/mac/BlockExceptions.h"
 #include "platform/mac/NSScrollerImpDetails.h"
 #include "platform/scroll/ScrollView.h"
 #include "platform/scroll/ScrollableArea.h"
 #include "platform/scroll/ScrollbarTheme.h"
 #include "platform/scroll/ScrollbarThemeMacCommon.h"
 #include "platform/scroll/ScrollbarThemeMacOverlayAPI.h"
 #include "wtf/MainThread.h"
@@ skipping 243 matching lines @@
 
 @end
 
 enum FeatureToAnimate {
     ThumbAlpha,
     TrackAlpha,
     UIStateTransition,
     ExpansionTransition
 };
 
-@interface WebScrollbarPartAnimation : NSAnimation
-{
+@class WebScrollbarPartAnimation;
+
+class WebScrollbarPartAnimationTimer {

[Alexei Svitkine (slow), 2014/09/03 15:39:35]

Can you add a comment on the class briefly summarizing its purpose (i.e. to
provide functionality of NSAnimation without a connection to the window server).

[Alexei Svitkine (slow), 2014/09/03 15:39:36]

Nit: Not sure on Blink style, but maybe this should be in an anon namespace?

[Robert Sesek, 2014/09/03 16:51:11]

I codesearched and it seems mostly to be for tests that anon is used. I did move
this into the blink:: namespace below, though.

[Robert Sesek, 2014/09/03 16:51:11]

Done.

+public:
+    WebScrollbarPartAnimationTimer(WebScrollbarPartAnimation* animation,
+                                   CFTimeInterval duration)
+        : m_timer(this, &WebScrollbarPartAnimationTimer::timerFired)
+        , m_startTime(0.0)
+        , m_duration(duration)
+        , m_animation(animation)
+        , m_timingFunction(CubicBezierTimingFunction::preset(CubicBezierTimingFunction::EaseInOut))
+    {
+    }
+
+    ~WebScrollbarPartAnimationTimer() {}
+
+    void start()
+    {
+        m_startTime = CACurrentMediaTime();
+        m_timer.startRepeating(1.0 / 35.0, FROM_HERE);

[Alexei Svitkine (slow), 2014/09/03 15:39:35]

Nit: Can you add a comment about where this constant comes from? If it matches
what the system libraries do, have you checked whether it's consistent between
different OS versions?

[Robert Sesek, 2014/09/03 16:51:11]

Done. All OS versions use a framerate of 60Hz, though I determined that 35 Hz is
sufficient for these animations.

+    }
+
+    void stop()
+    {
+        m_timer.stop();
+        [m_animation setCurrentProgress:1];
+    }
+
+    void setDuration(CFTimeInterval duration)
+    {
+        m_duration = duration;
+    }
+
+private:
+    void timerFired(Timer<WebScrollbarPartAnimationTimer>*)
+    {
+        CFTimeInterval currentTime = CACurrentMediaTime();
+        CFTimeInterval delta = currentTime - m_startTime;
+
+        if (delta >= m_duration) {
+            stop();
+            return;
+        }
+
+        double fraction = delta / m_duration;
+        double progress = m_timingFunction->evaluate(fraction, 0.001);
+        [m_animation setCurrentProgress:progress];
+    }
+
+    Timer<WebScrollbarPartAnimationTimer> m_timer;
+    CFTimeInterval m_startTime;
+    CFTimeInterval m_duration;
+    WebScrollbarPartAnimation* m_animation;
+    CubicBezierTimingFunction* m_timingFunction;
+};
+
+@interface WebScrollbarPartAnimation : NSObject {
     Scrollbar* _scrollbar;
+    OwnPtr<WebScrollbarPartAnimationTimer> _timer;
     RetainPtr<ScrollbarPainter> _scrollbarPainter;
     FeatureToAnimate _featureToAnimate;
     CGFloat _startValue;
     CGFloat _endValue;
 }
 - (id)initWithScrollbar:(Scrollbar*)scrollbar featureToAnimate:(FeatureToAnimate)featureToAnimate animateFrom:(CGFloat)startValue animateTo:(CGFloat)endValue duration:(NSTimeInterval)duration;
 @end
 
 @implementation WebScrollbarPartAnimation
 
 - (id)initWithScrollbar:(Scrollbar*)scrollbar featureToAnimate:(FeatureToAnimate)featureToAnimate animateFrom:(CGFloat)startValue animateTo:(CGFloat)endValue duration:(NSTimeInterval)duration
 {
-    self = [super initWithDuration:duration animationCurve:NSAnimationEaseInOut];
+    self = [super init];
     if (!self)
         return nil;
 
+    _timer = adoptPtr(new WebScrollbarPartAnimationTimer(self, duration));
     _scrollbar = scrollbar;
     _featureToAnimate = featureToAnimate;
     _startValue = startValue;
     _endValue = endValue;
 
-    [self setAnimationBlockingMode:NSAnimationNonblocking];
-
     return self;
 }
 
 - (void)startAnimation
 {
     ASSERT(_scrollbar);
 
     _scrollbarPainter = scrollbarPainterForScrollbar(_scrollbar);
+    _timer->start();
+}
 
-    [super startAnimation];
+- (void)stopAnimation
+{
+    _timer->stop();
+}
+
+- (void)setDuration:(CFTimeInterval)duration
+{
+    _timer->setDuration(duration);
 }
 
 - (void)setStartValue:(CGFloat)startValue
 {
     _startValue = startValue;
 }
 
 - (void)setEndValue:(CGFloat)endValue
 {
     _endValue = endValue;
 }
 
 - (void)setCurrentProgress:(NSAnimationProgress)progress
 {
-    [super setCurrentProgress:progress];
-
     ASSERT(_scrollbar);
 
     CGFloat currentValue;
     if (_startValue > _endValue)
         currentValue = 1 - progress;
     else
         currentValue = progress;
 
     switch (_featureToAnimate) {
     case ThumbAlpha:
@@ skipping 930 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return ScrollbarThemeMacCommon::isOverlayAPIAvailable();
 }
 
 } // namespace blink