Allow creation of 420 Buffer using YUV data.

There currently are no Objective-C API's to create a buffer with that data.
This change allows us to create a buffer with yuv data.

Bug: webrtc:9167
Change-Id: I00f1b91b04bbaa013a88137d0f54bef44287c5aa
Reviewed-on: https://webrtc-review.googlesource.com/70563
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Zeke Chin <tkchin@webrtc.org>
Commit-Queue: Peter Slatala <psla@google.com>
Cr-Commit-Position: refs/heads/master@{#22945}

sdk/objc/Framework/Classes/Video/RTCI420Buffer.mm

@@ -30,6 +30,18 @@
   return self;
 }
 
+- (instancetype)initWithWidth:(int)width
+                       height:(int)height
+                        dataY:(const uint8_t *)dataY
+                        dataU:(const uint8_t *)dataU
+                        dataV:(const uint8_t *)dataV {
+  if (self = [super init]) {
+    _i420Buffer = webrtc::I420Buffer::Copy(
+        width, height, dataY, width, dataU, (width + 1) / 2, dataV, (width + 1) / 2);
+  }
+  return self;
+}
+
 - (instancetype)initWithWidth:(int)width
                        height:(int)height
                       strideY:(int)strideY

sdk/objc/Framework/Headers/WebRTC/RTCVideoFrameBuffer.h

@@ -38,6 +38,11 @@ RTC_EXPORT
 @property(nonatomic, readonly) int strideU;
 @property(nonatomic, readonly) int strideV;
 
+- (instancetype)initWithWidth:(int)width
+                       height:(int)height
+                        dataY:(const uint8_t *)dataY
+                        dataU:(const uint8_t *)dataU
+                        dataV:(const uint8_t *)dataV;
 - (instancetype)initWithWidth:(int)width height:(int)height;
 - (instancetype)initWithWidth:(int)width
                        height:(int)height