Add JavaI420Buffer to the API.

This renames I420BufferImpl to JavaI420Buffer and moves it as part of
the API.

Bug: webrtc:7749
Change-Id: I70726f248ba4601b4922996712bdfdafbfa4a1e1
Reviewed-on: https://webrtc-review.googlesource.com/5381
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20145}
diff --git a/sdk/android/api/org/webrtc/VideoRenderer.java b/sdk/android/api/org/webrtc/VideoRenderer.java
index e44578c..182093c 100644
--- a/sdk/android/api/org/webrtc/VideoRenderer.java
+++ b/sdk/android/api/org/webrtc/VideoRenderer.java
@@ -163,7 +163,7 @@
         VideoRenderer.renderFrameDone(this);
         buffer = backingBuffer;
       } else if (yuvFrame) {
-        buffer = new I420BufferImpl(width, height, yuvPlanes[0], yuvStrides[0], yuvPlanes[1],
+        buffer = JavaI420Buffer.wrap(width, height, yuvPlanes[0], yuvStrides[0], yuvPlanes[1],
             yuvStrides[1], yuvPlanes[2], yuvStrides[2],
             () -> { VideoRenderer.renderFrameDone(this); });
       } else {