Libvpx: configure a way in Medialib to drop frames instead of video lag.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=153858804

extensions/vp9/src/main/java/com/google/android/exoplayer2/ext/vp9/LibvpxVideoRenderer.java

@@ -262,11 +262,11 @@ public final class LibvpxVideoRenderer extends BaseRenderer {
       return false;
     }
 
-    // Drop the frame if we're joining and are more than 30ms late, or if we have the next frame
-    // and that's also late. Else we'll render what we have.
-    if ((joiningDeadlineMs != C.TIME_UNSET && outputBuffer.timeUs < positionUs - 30000)
-        || (nextOutputBuffer != null && !nextOutputBuffer.isEndOfStream()
-        && nextOutputBuffer.timeUs < positionUs)) {
+    final long nextOutputBufferTimeUs =
+        nextOutputBuffer != null && !nextOutputBuffer.isEndOfStream()
+            ? nextOutputBuffer.timeUs : C.TIME_UNSET;
+    if (shouldDropOutputBuffer(
+        outputBuffer.timeUs, nextOutputBufferTimeUs, positionUs, joiningDeadlineMs)) {
       dropBuffer();
       return true;
     }
@@ -280,6 +280,25 @@ public final class LibvpxVideoRenderer extends BaseRenderer {
     return false;
   }
 
+
+  /**
+   * Returns whether the current frame should be dropped.
+   *
+   * @param outputBufferTimeUs The timestamp of the current output buffer.
+   * @param nextOutputBufferTimeUs The timestamp of the next output buffer or
+   *     {@link TIME_UNSET} if the next output buffer is unavailable.
+   * @param positionUs The current playback position.
+   * @param joiningDeadlineMs The joining deadline.
+   * @return Returns whether to drop the current output buffer.
+   */
+  protected boolean shouldDropOutputBuffer(long outputBufferTimeUs, long nextOutputBufferTimeUs,
+      long positionUs, long joiningDeadlineMs) {
+     // Drop the frame if we're joining and are more than 30ms late, or if we have the next frame
+     // and that's also late. Else we'll render what we have.
+    return (joiningDeadlineMs != C.TIME_UNSET && outputBufferTimeUs < positionUs - 30000)
+        || (nextOutputBufferTimeUs != C.TIME_UNSET && nextOutputBufferTimeUs < positionUs);
+  }
+
   private void renderBuffer() {
     int bufferMode = outputBuffer.mode;
     boolean renderRgb = bufferMode == VpxDecoder.OUTPUT_MODE_RGB && surface != null;