iOS: Add interface for injecting custom shaders

webrtc/sdk/objc/Framework/Classes/RTCDefaultShader.h

Index: webrtc/sdk/objc/Framework/Classes/RTCDefaultShader.h
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCNV12TextureCache.h b/webrtc/sdk/objc/Framework/Classes/RTCDefaultShader.h
similarity index 58%
copy from webrtc/sdk/objc/Framework/Classes/RTCNV12TextureCache.h
copy to webrtc/sdk/objc/Framework/Classes/RTCDefaultShader.h
index 0aa7a5718177b01678622b550cc001fdb290bd31..3e6b759de893a8fcf5a8663d410aab6e6d397aa7 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCNV12TextureCache.h
+++ b/webrtc/sdk/objc/Framework/Classes/RTCDefaultShader.h
@@ -8,22 +8,15 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#import <GLKit/GLKit.h>
-
-@class RTCVideoFrame;
+#import "WebRTC/RTCVideoViewShader.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface RTCNV12TextureCache : NSObject
-
-@property(nonatomic, readonly) GLuint yTexture;
-@property(nonatomic, readonly) GLuint uvTexture;
-
-- (nullable instancetype)initWithContext:(EAGLContext *)context;
-
-- (BOOL)uploadFrameToTextures:(RTCVideoFrame *)frame;
-
-- (void)releaseTextures;
+/** Default RTCVideoViewShader that will be used in RTCNSGLVideoView and
+ *  RTCEAGLVideoView if no external shader is specified. This shader will render
+ *  the video in a rectangle without any color or geometric transformations.
+ */
+@interface RTCDefaultShader : NSObject<RTCVideoViewShader>
 
 @end