Fix OSX 10.12 compilation errors in chrome/browser/ui.

chrome/browser/ui/cocoa/animatable_image.mm

Index: chrome/browser/ui/cocoa/animatable_image.mm
diff --git a/chrome/browser/ui/cocoa/animatable_image.mm b/chrome/browser/ui/cocoa/animatable_image.mm
index 4af6be8ef3c92756c854456fd5cb357d73d4bcee..4fbc1f07284c69217760df3c7328323b9f00104a 100644
--- a/chrome/browser/ui/cocoa/animatable_image.mm
+++ b/chrome/browser/ui/cocoa/animatable_image.mm
@@ -5,8 +5,12 @@
 #import "chrome/browser/ui/cocoa/animatable_image.h"
 
 #include "base/logging.h"
+#import "base/mac/sdk_forward_declarations.h"
 #import "third_party/google_toolbox_for_mac/src/AppKit/GTMNSAnimation+Duration.h"
 
+@interface AnimatableImage (Private) <CAAnimationDelegate>
+@end
+
 @implementation AnimatableImage
 
 @synthesize startFrame = startFrame_;
@@ -121,6 +125,9 @@
   [CATransaction commit];
 }
 
+- (void)animationDidStart:(CAAnimation*)animation {
+}
+
 // CAAnimation delegate method called when the animation is complete.
 - (void)animationDidStop:(CAAnimation*)animation finished:(BOOL)flag {
   // Close the window, releasing self.