[Audio Focus] Add no enforce flag

Adds an audio focus flag that enables audio focus manager but
disables enforcement of a single media session. This gives us
the option of enabling audio focus tracking without the user
facing change of enforcing a single media session.

BUG=875004

Change-Id: I5415ec76db7b22d4d91ea98c92e3f1515d9df97b
Reviewed-on: https://chromium-review.googlesource.com/c/1231915
Commit-Queue: Becca Hughes <[email protected]>
Reviewed-by: Tommy Steimel <[email protected]>
Cr-Commit-Position: refs/heads/master@{#596446}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 60fc0a63..ed02c38 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -801,6 +801,9 @@
      media_session::switches::kEnableAudioFocus,
      media_session::switches::kEnableAudioFocusDuckFlash},
 #endif  // BUILDFLAG(ENABLE_PLUGINS)
+    {flag_descriptions::kEnableAudioFocusEnabledNoEnforce,
+     media_session::switches::kEnableAudioFocus,
+     media_session::switches::kEnableAudioFocusNoEnforce},
 };
 #endif  // !defined(OS_ANDROID)