Android: Don't create VP9 encoder/decoder when not supported.

In the SoftwareVideoCodecFactories, don't try to create VP9 encoder or
decoder if WebRTC was built without support for it.

Bug: None
Change-Id: I09b87fdcf798c763310af4998dbea8011843010d
Reviewed-on: https://webrtc-review.googlesource.com/22924
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20672}

sdk/android/api/org/webrtc/SoftwareVideoDecoderFactory.java

@@ -16,7 +16,7 @@ public class SoftwareVideoDecoderFactory implements VideoDecoderFactory {
     if (codecType.equalsIgnoreCase("VP8")) {
       return new VP8Decoder();
     }
-    if (codecType.equalsIgnoreCase("VP9")) {
+    if (codecType.equalsIgnoreCase("VP9") && VP9Decoder.isSupported()) {
       return new VP9Decoder();
     }