Add an additional VDA::Flush() mode to return all allocated buffers.

content/common/gpu/media/android_video_decode_accelerator.cc

Index: content/common/gpu/media/android_video_decode_accelerator.cc
diff --git a/content/common/gpu/media/android_video_decode_accelerator.cc b/content/common/gpu/media/android_video_decode_accelerator.cc
index c097811c2d3d82186cb110012a6807a431631df4..5b48d6075f9eb0b23084e34238e22035d6fccf22 100644
--- a/content/common/gpu/media/android_video_decode_accelerator.cc
+++ b/content/common/gpu/media/android_video_decode_accelerator.cc
@@ -332,6 +332,11 @@ bool AndroidVideoDecodeAccelerator::Initialize(const Config& config,
     return false;
   }
 
+  if (config.flush_mode != Config::FlushMode::KEEP_OUTPUT_BUFFERS) {
+    NOTIMPLEMENTED() << "Modes other than KEEP_OUTPUT_BUFFERS not implemented";
+    return false;
+  }
+
   DCHECK(client);
   client_ = client;
   codec_config_ = new CodecConfig();