Add group_id member in ForwardingAudioStreamFactory

Actually using it is TODO.

No-Try: true
Bug: 824019
Change-Id: I9053827dba2504218559be523574b71ef079c72b
Reviewed-on: https://chromium-review.googlesource.com/1046646
Commit-Queue: Max Morin <maxmorin@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556421}

content/browser/media/forwarding_audio_stream_factory.cc

@@ -23,7 +23,8 @@ ForwardingAudioStreamFactory::ForwardingAudioStreamFactory(
     std::unique_ptr<AudioStreamBrokerFactory> broker_factory)
     : WebContentsObserver(web_contents),
       connector_(std::move(connector)),
-      broker_factory_(std::move(broker_factory)) {
+      broker_factory_(std::move(broker_factory)),
+      group_id_(base::UnguessableToken::Create()) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK(web_contents);
   DCHECK(broker_factory_);

content/browser/media/forwarding_audio_stream_factory.h

@@ -11,6 +11,7 @@
 #include "base/containers/flat_set.h"
 #include "base/containers/unique_ptr_adapters.h"
 #include "base/macros.h"
+#include "base/unguessable_token.h"
 #include "content/browser/media/audio_stream_broker.h"
 #include "content/common/content_export.h"
 #include "content/common/media/renderer_audio_input_stream_factory.mojom.h"
@@ -42,6 +43,8 @@ class CONTENT_EXPORT ForwardingAudioStreamFactory final
 
   ~ForwardingAudioStreamFactory() final;
 
+  const base::UnguessableToken& group_id() { return group_id_; }
+
   // TODO(https://crbug.com/803102): Add loopback and muting streams.
   // TODO(https://crbug.com/787806): Automatically restore streams on audio
   // service restart.
@@ -81,6 +84,11 @@ class CONTENT_EXPORT ForwardingAudioStreamFactory final
   const std::unique_ptr<service_manager::Connector> connector_;
   const std::unique_ptr<AudioStreamBrokerFactory> broker_factory_;
 
+  // Unique id indentifying all streams belonging to the WebContents owning
+  // |this|.
+  // TODO(https://crbug.com/824019): Use this for loopback.
+  const base::UnguessableToken group_id_;
+
   // Lazily acquired. Reset on connection error and when we no longer have any
   // streams. Note: we don't want muting to force the connection to be open,
   // since we want to clean up the service when not in use. If we have active