Revert of Remove disable-app-list-voice-search flag. (https://codereview.chromium.org/353793003/)

Reason for revert:
Caused compile error on Blink GPU Mac Builder:
http://build.chromium.org/p/chromium.webkit/builders/GPU%20Mac%20Builder

Original issue's description:
> Remove disable-app-list-voice-search flag.
> 
> BUG=367341
> R=xiyuan@chromium.org
> TEST=compile
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281904

TBR=xiyuan@chromium.org,mukai@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=367341

Review URL: https://codereview.chromium.org/379673003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281908 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/about_flags.cc

@@ -1526,6 +1526,13 @@ const Experiment kExperiments[] = {
     kOsLinux | kOsWin | kOsCrOS,
     SINGLE_VALUE_TYPE(app_list::switches::kDisableAppInfo)
   },
+  {
+    "disable-app-list-voice-search",
+    IDS_FLAGS_DISABLE_APP_LIST_VOICE_SEARCH,
+    IDS_FLAGS_DISABLE_APP_LIST_VOICE_SEARCH_DESCRIPTION,
+    kOsCrOS,
+    SINGLE_VALUE_TYPE(app_list::switches::kDisableVoiceSearch)
+  },
   {
     "enable-drive-apps-in-app-list",
     IDS_FLAGS_ENABLE_DRIVE_APPS_IN_APP_LIST_NAME,

ui/app_list/app_list_switches.cc

@@ -15,6 +15,9 @@ const char kDisableAppInfo[] = "disable-app-list-app-info";
 // Disables syncing of the app list independent of extensions.
 const char kDisableSyncAppList[] = "disable-sync-app-list";
 
+// If set, the voice search is disabled in app list UI.
+const char kDisableVoiceSearch[] = "disable-app-list-voice-search";
+
 // If set, the app list will be centered and wide instead of tall.
 const char kEnableCenteredAppList[] = "enable-centered-app-list";
 
@@ -48,7 +51,7 @@ bool IsFolderUIEnabled() {
 bool IsVoiceSearchEnabled() {
   // Speech recognition in AppList is only for ChromeOS right now.
 #if defined(OS_CHROMEOS)
-  return true;
+  return !CommandLine::ForCurrentProcess()->HasSwitch(kDisableVoiceSearch);
 #else
   return false;
 #endif

ui/app_list/app_list_switches.h

@@ -13,6 +13,7 @@ namespace switches {
 // Please keep these flags sorted.
 APP_LIST_EXPORT extern const char kDisableAppInfo[];
 APP_LIST_EXPORT extern const char kDisableSyncAppList[];
+APP_LIST_EXPORT extern const char kDisableVoiceSearch[];
 APP_LIST_EXPORT extern const char kEnableCenteredAppList[];
 APP_LIST_EXPORT extern const char kEnableDriveAppsInAppList[];
 APP_LIST_EXPORT extern const char kEnableExperimentalAppList[];