Add --enable-usermedia-screen-capturing in about:flags

Then new flag allows to enable screen capture support for getUserMedia().

BUG=134249

Review URL: https://codereview.chromium.org/12211065

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@181405 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 408120b1..ba248e3 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1289,6 +1289,13 @@
     kOsWin | kOsCrOS | kOsLinux,
     SINGLE_VALUE_TYPE(switches::kEnableSyncDictionary)
   },
+  {
+    "enable-usermedia-screen-capture",
+    IDS_FLAGS_ENABLE_SCREEN_CAPTURE_NAME,
+    IDS_FLAGS_ENABLE_SCREEN_CAPTURE_DESCRIPTION,
+    kOsDesktop,
+    SINGLE_VALUE_TYPE(switches::kEnableUserMediaScreenCapturing)
+  },
 };
 
 const Experiment* experiments = kExperiments;