MSE: Clarify WebMediaSource::AddSourceBuffer() method

For this interface method and implementation, adds comments, renames
|type| parameter to |content_type|, and removes unnecessary .data()
following Utf8(); all per CR comments on the recently added similar
WebSourceBuffer::{Can}ChangeType() methods.

BUG=605134

Change-Id: I0cd259a1a1508edff91287eb60b49721d61e9187
Reviewed-on: https://chromium-review.googlesource.com/1115578Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570836}

media/blink/webmediasource_impl.cc

@@ -32,13 +32,13 @@ WebMediaSourceImpl::WebMediaSourceImpl(ChunkDemuxer* demuxer)
 WebMediaSourceImpl::~WebMediaSourceImpl() = default;
 
 WebMediaSource::AddStatus WebMediaSourceImpl::AddSourceBuffer(
-    const blink::WebString& type,
+    const blink::WebString& content_type,
     const blink::WebString& codecs,
     blink::WebSourceBuffer** source_buffer) {
   std::string id = base::GenerateGUID();
 
   WebMediaSource::AddStatus result = static_cast<WebMediaSource::AddStatus>(
-      demuxer_->AddId(id, type.Utf8().data(), codecs.Utf8().data()));
+      demuxer_->AddId(id, content_type.Utf8(), codecs.Utf8()));
 
   if (result == WebMediaSource::kAddStatusOk)
     *source_buffer = new WebSourceBufferImpl(id, demuxer_);

media/blink/webmediasource_impl.h

@@ -21,7 +21,7 @@ class MEDIA_BLINK_EXPORT WebMediaSourceImpl : public blink::WebMediaSource {
   ~WebMediaSourceImpl() override;
 
   // blink::WebMediaSource implementation.
-  AddStatus AddSourceBuffer(const blink::WebString& type,
+  AddStatus AddSourceBuffer(const blink::WebString& content_type,
                             const blink::WebString& codecs,
                             blink::WebSourceBuffer** source_buffer) override;
   double Duration() override;

third_party/blink/public/platform/web_media_source.h

@@ -54,9 +54,24 @@ class WebMediaSource {
   };
 
   virtual ~WebMediaSource() = default;
-  virtual AddStatus AddSourceBuffer(const WebString& type,
+
+  // Attempts to create a new WebSourceBuffer for use with this WebMediaSource.
+  // |content_type| is the ContentType string of the new WebSourceBuffer
+  // bytestream's MIME type, and |codecs| contains the "codecs" parameter
+  // string, if any, of the bytestream's MIME type.
+  // If this WebMediaSource supports the format indicated by |content_type| and
+  // |codecs| and has enough resources to support a new WebSourceBuffer, returns
+  // kAddStatusOk and creates a new WebSourceBuffer and changes the
+  // WebSourceBuffer parameter to point to it.
+  // If this WebMediaSource cannot handle another WebSourceBuffer right now,
+  // returns kAddStatusReachedIdLimit without modifying the WebSourceBuffer
+  // parameter.
+  // If |content_type| and |codecs| are not supported, returns
+  // kAddStatusNotSupported without modifying the WebSourceBuffer parameter.
+  virtual AddStatus AddSourceBuffer(const WebString& content_type,
                                     const WebString& codecs,
                                     WebSourceBuffer**) = 0;
+
   virtual double Duration() = 0;
   virtual void SetDuration(double) = 0;
   virtual void MarkEndOfStream(EndOfStreamStatus) = 0;