Mac Video Capture: expose --enable-avfoundation as tristate in chrome://flags

Currently chrome://flags only exposes #enable-avfoundation as an enable
link. This CL exposes instead a tristate compose of Default/Enable/Disable.



BUG=356106, 396764

Review URL: https://codereview.chromium.org/460113006

Cr-Commit-Position: refs/heads/master@{#289053}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289053 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/about_flags.cc

@@ -489,6 +489,14 @@ const Experiment::Choice kEnableDropSyncCredentialChoices[] = {
     password_manager::switches::kDisableDropSyncCredential, "" },
 };
 
+#if defined(OS_MACOSX)
+const Experiment::Choice kEnableAVFoundationChoices[] = {
+  { IDS_GENERIC_EXPERIMENT_CHOICE_DEFAULT, "", "" },
+  { IDS_GENERIC_EXPERIMENT_CHOICE_ENABLED, switches::kEnableAVFoundation, ""},
+  { IDS_GENERIC_EXPERIMENT_CHOICE_DISABLED, switches::kForceQTKit, ""}
+};
+#endif
+
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the experiment is the internal name. If you'd like to
@@ -1214,7 +1222,7 @@ const Experiment kExperiments[] = {
     IDS_FLAGS_ENABLE_AVFOUNDATION_NAME,
     IDS_FLAGS_ENABLE_AVFOUNDATION_DESCRIPTION,
     kOsMac,
-    SINGLE_VALUE_TYPE(switches::kEnableAVFoundation)
+    MULTI_VALUE_TYPE(kEnableAVFoundationChoices)
   },
 #endif
   {

media/video/capture/mac/avfoundation_glue.mm

@@ -120,9 +120,6 @@ bool AVFoundationGlue::IsAVFoundationSupported() {
     return false;
 
   // Next in precedence is the enable-avfoundation flag.
-  // TODO(mcasas,vrk): There should be 3 states of AVFoundation: user forced on,
-  // user forced off (i.e. force QTKit), and default (respect field trial).
-  // crbug.com/396764
   // TODO(vrk): Does this really need to be static?
   static bool should_enable_avfoundation =
       command_line->HasSwitch(switches::kEnableAVFoundation) ||