Reland "[Audio Focus] Restrict browser group to CrOS"

This is a reland of 858e896d

Original change's description:
> [Audio Focus] Restrict browser group to CrOS
>
> Restrict browser audio focus grouping to Chrome OS.
>
> BUG=915501
>
> Change-Id: I702952cca7a388e78c201531866307797d25b277
> Reviewed-on: https://chromium-review.googlesource.com/c/1379918
> Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
> Commit-Queue: Becca Hughes <beccahughes@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#617800}

Bug: 915501
Change-Id: Ideb9814a6d4ff7e9faedc66efa6d2073adec818d
Reviewed-on: https://chromium-review.googlesource.com/c/1386107Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619747}

chrome/browser/web_applications/extensions/web_app_audio_focus_browsertest.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/macros.h"
+#include "base/test/scoped_feature_list.h"
 #include "chrome/browser/extensions/browsertest_util.h"
 #include "chrome/browser/extensions/extension_browsertest.h"
 #include "chrome/browser/ui/browser.h"
@@ -13,6 +14,7 @@
 #include "content/public/test/browser_test_utils.h"
 #include "extensions/test/extension_test_message_listener.h"
 #include "extensions/test/test_extension_dir.h"
+#include "media/base/media_switches.h"
 #include "services/media_session/public/cpp/switches.h"
 
 namespace web_app {
@@ -34,6 +36,8 @@ class WebAppAudioFocusBrowserTest : public extensions::ExtensionBrowserTest {
   void SetUpCommandLine(base::CommandLine* command_line) override {
     InProcessBrowserTest::SetUpCommandLine(command_line);
     command_line->AppendSwitch(media_session::switches::kEnableAudioFocus);
+    scoped_feature_list_.InitAndEnableFeature(
+        media::kUseGroupedBrowserAudioFocus);
   }
 
   bool IsPaused(content::WebContents* web_contents) {
@@ -74,6 +78,8 @@ class WebAppAudioFocusBrowserTest : public extensions::ExtensionBrowserTest {
   }
 
  private:
+  base::test::ScopedFeatureList scoped_feature_list_;
+
   DISALLOW_COPY_AND_ASSIGN(WebAppAudioFocusBrowserTest);
 };
 

content/browser/media/session/audio_focus_delegate_default.cc

@@ -6,9 +6,11 @@
 
 #include "base/no_destructor.h"
 #include "base/unguessable_token.h"
+#include "build/build_config.h"
 #include "content/browser/media/session/media_session_impl.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/service_manager_connection.h"
+#include "media/base/media_switches.h"
 #include "services/media_session/public/cpp/switches.h"
 #include "services/media_session/public/mojom/audio_focus.mojom.h"
 #include "services/media_session/public/mojom/constants.mojom.h"
@@ -22,10 +24,20 @@ namespace {
 
 const char kAudioFocusSourceName[] = "web";
 
-static const base::UnguessableToken& GetBrowserGroupId() {
-  static const base::NoDestructor<base::UnguessableToken> token(
-      base::UnguessableToken::Create());
-  return *token;
+base::UnguessableToken GetAudioFocusGroupId(MediaSessionImpl* session) {
+  // Allow the media session to override the group id.
+  if (session->audio_focus_group_id() != base::UnguessableToken::Null())
+    return session->audio_focus_group_id();
+
+  // If it is enabled then use a shared audio focus group id for the whole
+  // browser. This will mean that tabs will share audio focus.
+  if (base::FeatureList::IsEnabled(media::kUseGroupedBrowserAudioFocus)) {
+    static const base::NoDestructor<base::UnguessableToken> token(
+        base::UnguessableToken::Create());
+    return *token;
+  }
+
+  return base::UnguessableToken::Create();
 }
 
 // AudioFocusDelegateDefault is the default implementation of
@@ -102,9 +114,7 @@ AudioFocusDelegateDefault::RequestAudioFocus(AudioFocusType audio_focus_type) {
     audio_focus_ptr_->RequestGroupedAudioFocus(
         mojo::MakeRequest(&request_client_ptr_), std::move(media_session),
         session_info_.Clone(), audio_focus_type,
-        media_session_->audio_focus_group_id() == base::UnguessableToken::Null()
-            ? GetBrowserGroupId()
-            : media_session_->audio_focus_group_id(),
+        GetAudioFocusGroupId(media_session_),
         base::BindOnce(&AudioFocusDelegateDefault::FinishAudioFocusRequest,
                        base::Unretained(this), audio_focus_type));
   }

content/browser/media/session/audio_focus_delegate_default_browsertest.cc

@@ -4,12 +4,14 @@
 
 #include "base/command_line.h"
 #include "base/unguessable_token.h"
+#include "build/build_config.h"
 #include "content/browser/media/session/media_session_impl.h"
 #include "content/browser/media/session/mock_media_session_player_observer.h"
 #include "content/public/common/service_manager_connection.h"
 #include "content/public/test/content_browser_test.h"
 #include "content/shell/browser/shell.h"
 #include "media/base/media_content_type.h"
+#include "media/base/media_switches.h"
 #include "services/media_session/public/cpp/switches.h"
 #include "services/media_session/public/cpp/test/audio_focus_test_util.h"
 #include "services/media_session/public/cpp/test/mock_media_session.h"
@@ -106,7 +108,8 @@ class AudioFocusDelegateDefaultBrowserTest : public ContentBrowserTest {
       media_session::test::MockMediaSessionMojoObserver observer(
           *media_session);
       observer.WaitForState(
-          use_separate_group_id
+          use_separate_group_id || !base::FeatureList::IsEnabled(
+                                       media::kUseGroupedBrowserAudioFocus)
               ? media_session::mojom::MediaSessionInfo::SessionState::kSuspended
               : media_session::mojom::MediaSessionInfo::SessionState::kActive);
     }

media/base/media_switches.cc

@@ -500,4 +500,15 @@ bool IsVideoCaptureAcceleratedJpegDecodingEnabled() {
   return false;
 }
 
+// Enable grouped browser audio focus. This means that all browser media
+// sessions will share audio focus. This should only be enabled on Chrome OS.
+const base::Feature kUseGroupedBrowserAudioFocus {
+  "UseGroupedBrowserAudioFocus",
+#if defined(OS_CHROMEOS)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
+
 }  // namespace media

media/base/media_switches.h

@@ -132,6 +132,7 @@ MEDIA_EXPORT extern const base::Feature kSpecCompliantCanPlayThrough;
 MEDIA_EXPORT extern const base::Feature kUnifiedAutoplay;
 MEDIA_EXPORT extern const base::Feature kUseAndroidOverlay;
 MEDIA_EXPORT extern const base::Feature kUseAndroidOverlayAggressively;
+MEDIA_EXPORT extern const base::Feature kUseGroupedBrowserAudioFocus;
 MEDIA_EXPORT extern const base::Feature kUseModernMediaControls;
 MEDIA_EXPORT extern const base::Feature kUseNewMediaCache;
 MEDIA_EXPORT extern const base::Feature kUseR16Texture;