[webcodecs] Add 'required' where missing from IDL dicts

Updates a few WebCodecs IDL dictionary types to use the 'required'
attribute where the draft spec indicates. In particular, it updates
AudioFrameInit, EncodedAudioChunkInit, and EncodedVideoChunkInit to
enforce the required fields are populated.

I also looked at making similar change to VideoDecoderConfig, but the
codedWidth and codedHeight fields' usage in the implementation already
has notes that go deeper (AVCC coherence is TBD, for example).

Also includes a change to make EncodedVideoChunkInit.duration _not_
nullable. It is not required, so its absence is sufficient to indicate
it is unset. Retains the nullable attribute on the readonly
EncodedVideoChunk.duration field.

BUG=1149028

Change-Id: If82c495d94ed9532007dfda614ec97bc88e773ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2543126Reviewed-by: Eugene Zemtsov <eugene@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828477}

third_party/blink/renderer/modules/webcodecs/audio_frame_init.idl

@@ -5,6 +5,6 @@
 // https://github.com/WICG/web-codecs
 
 dictionary AudioFrameInit {
-  unsigned long long timestamp;  // microseconds
-  AudioBuffer buffer;
+  required unsigned long long timestamp;  // microseconds
+  required AudioBuffer buffer;
 };

third_party/blink/renderer/modules/webcodecs/encoded_audio_chunk_init.idl

@@ -5,7 +5,7 @@
 // https://github.com/WICG/web-codecs
 
 dictionary EncodedAudioChunkInit {
-  EncodedVideoChunkType type;
-  unsigned long long timestamp; // microseconds
-  BufferSource data;
+  required EncodedVideoChunkType type;
+  required unsigned long long timestamp; // microseconds
+  required BufferSource data;
 };

third_party/blink/renderer/modules/webcodecs/encoded_video_chunk.cc

@@ -17,9 +17,8 @@ EncodedVideoChunk* EncodedVideoChunk::Create(EncodedVideoChunkInit* init) {
   EncodedVideoMetadata metadata;
   metadata.timestamp = base::TimeDelta::FromMicroseconds(init->timestamp());
   metadata.key_frame = (init->type() == "key");
-  if (init->hasDurationNonNull()) {
-    metadata.duration =
-        base::TimeDelta::FromMicroseconds(init->durationNonNull());
+  if (init->hasDuration()) {
+    metadata.duration = base::TimeDelta::FromMicroseconds(init->duration());
   }
   DOMArrayPiece piece(init->data());
 

third_party/blink/renderer/modules/webcodecs/encoded_video_chunk_init.idl

@@ -5,8 +5,8 @@
 // https://github.com/WICG/web-codecs
 
 dictionary EncodedVideoChunkInit {
-  EncodedVideoChunkType type;
-  unsigned long long timestamp; // microseconds
-  unsigned long long? duration;  // microseconds
-  BufferSource data;
+  required EncodedVideoChunkType type;
+  required unsigned long long timestamp; // microseconds
+  unsigned long long duration;  // microseconds
+  required BufferSource data;
 };