vp9: Expose libvpx build configuration

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127216536

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

@@ -131,6 +131,13 @@ public final class LibvpxVideoRenderer extends Renderer {
     return isLibvpxAvailable() ? VpxDecoder.getLibvpxVersion() : null;
   }
 
+  /**
+   * Returns the configuration string with which the underlying libvpx library was built.
+   */
+  public static String getLibvpxConfig() {
+    return isLibvpxAvailable() ? VpxDecoder.getLibvpxConfig() : null;
+  }
+
   @Override
   public int getTrackType() {
     return C.TRACK_TYPE_VIDEO;

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

@@ -52,6 +52,11 @@ import java.nio.ByteBuffer;
    */
   public static native String getLibvpxVersion();
 
+  /**
+   * Returns the configuration string with which the underlying libvpx library was built.
+   */
+  public static native String getLibvpxConfig();
+
   private final long vpxDecContext;
 
   private volatile int outputMode;

extensions/vp9/src/main/jni/vpx_jni.cc

@@ -170,6 +170,10 @@ FUNC(jstring, getLibvpxVersion) {
   return env->NewStringUTF(vpx_codec_version_str());
 }
 
+FUNC(jstring, getLibvpxConfig) {
+  return env->NewStringUTF(vpx_codec_build_config());
+}
+
 FUNC(jstring, vpxGetErrorMessage, jlong jContext) {
   vpx_codec_ctx_t* const context = reinterpret_cast<vpx_codec_ctx_t*>(jContext);
   return env->NewStringUTF(vpx_codec_error(context));