Mac: Add flag to force QTKit in otherwise AVFoundation-enabled builds/configs

media/base/media_switches.cc

Index: media/base/media_switches.cc
diff --git a/media/base/media_switches.cc b/media/base/media_switches.cc
index 68b6e5ef08f75bc7c8158e8b8f124033b59f7f06..515c0bc3d1af45fbebbfc629d9ca60886c88dedb 100644
--- a/media/base/media_switches.cc
+++ b/media/base/media_switches.cc
@@ -40,6 +40,11 @@ const char kAlsaOutputDevice[] = "alsa-output-device";
 // for experimentation purposes, in particular library load time issue, the
 // usage of this library can be enabled by using this flag.
 const char kEnableAVFoundation[] = "enable-avfoundation";
+// QTKit is the media capture API predecessor to AVFoundation, available up and
+// until Mac OS X 10.9 (despite being deprecated in this last one). This flag
+// is used for troubleshooting and testing, and forces QTKit in builds and
+// configurations where AVFoundation would be used otherwise.
+const char kForceQTKit[] = "force-qtkit";
 #endif
 
 #if defined(OS_WIN)