media: Add Feature to control External Clear Key key system support

chrome/browser/media/encrypted_media_browsertest.cc

Index: chrome/browser/media/encrypted_media_browsertest.cc
diff --git a/chrome/browser/media/encrypted_media_browsertest.cc b/chrome/browser/media/encrypted_media_browsertest.cc
index 4b197757f7165c0702fbe1fbb525186dd3f2fc67..96283b61266f0001eadc10a6b74539992ec7e6d3 100644
--- a/chrome/browser/media/encrypted_media_browsertest.cc
+++ b/chrome/browser/media/encrypted_media_browsertest.cc
@@ -27,6 +27,7 @@
 #if defined(ENABLE_PEPPER_CDMS)
 #include "chrome/browser/media/pepper_cdm_test_constants.h"
 #include "chrome/browser/media/pepper_cdm_test_helper.h"
+#include "media/base/media_switches.h"
 #endif
 
 #include "widevine_cdm_version.h"  //  In SHARED_INTERMEDIATE_DIR.
@@ -271,6 +272,8 @@ class EncryptedMediaTestBase : public MediaBrowserTest {
       RegisterPepperCdm(command_line, kClearKeyCdmBaseDirectory,
                         kClearKeyCdmAdapterFileName, kClearKeyCdmDisplayName,
                         kClearKeyCdmPepperMimeType);
+      command_line->AppendSwitchASCII(switches::kEnableFeatures,
+                                      media::kExternalClearKeyForTesting.name);
     }
 #endif  // defined(ENABLE_PEPPER_CDMS)
   }