Add Vp8FrameConfig::IntraFrame()

Simple function to check if the frame described by Vp8FrameConfig
will be an intra frame.

Bug: None
Change-Id: I0ba0476762a152e1be3711352024fc6e1bd35f12
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/133560
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27709}

api/video_codecs/vp8_frame_config.h

@@ -47,6 +47,12 @@ struct Vp8FrameConfig {
 
   bool Updates(Buffer buffer) const;
 
+  bool IntraFrame() const {
+    // Intra frames do not reference any buffers, and update all buffers.
+    return last_buffer_flags == kUpdate && golden_buffer_flags == kUpdate &&
+           arf_buffer_flags == kUpdate;
+  }
+
   bool drop_frame;
   BufferFlags last_buffer_flags;
   BufferFlags golden_buffer_flags;