[ASVideoNode] Addition of reset method to return to initial state (#2119)

* [ASVideoNode] Addition of reset method to allow video node to return to initial state of placeholder and play button

* Implemented pull request review comments for code style

AsyncDisplayKit/ASVideoNode.h

@@ -39,6 +39,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (void)play;
 - (void)pause;
 - (BOOL)isPlaying;
+- (void)resetToPlaceholder;
 
 @property (nullable, nonatomic, strong, readwrite) AVAsset *asset;
 /**

AsyncDisplayKit/ASVideoNode.mm

@@ -671,6 +671,19 @@ static NSString * const kRate = @"rate";
   return YES;
 }
 
+- (void)resetToPlaceholder
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  
+  if (_playerNode != nil) {
+    [_playerNode removeFromSupernode];
+    _playerNode = nil;
+  }
+  
+  [_player seekToTime:kCMTimeZero];
+  [self pause];
+}
+
 
 #pragma mark - Playback observers
 

AsyncDisplayKit/ASVideoPlayerNode.h

@@ -68,6 +68,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (void)play;
 - (void)pause;
 - (BOOL)isPlaying;
+- (void)resetToPlaceholder;
 
 @end
 

AsyncDisplayKit/ASVideoPlayerNode.mm

@@ -668,6 +668,11 @@ static void *ASVideoPlayerNodeContext = &ASVideoPlayerNodeContext;
   return [_videoNode isPlaying];
 }
 
+- (void)resetToPlaceholder
+{
+  [_videoNode resetToPlaceholder];
+}
+
 - (NSArray *)controlsForLayoutSpec
 {
   NSMutableArray *controls = [[NSMutableArray alloc] initWithCapacity:_cachedControls.count];