media: Add External Clear Key content browser test on Android

media/base/key_systems.cc

Index: media/base/key_systems.cc
diff --git a/media/base/key_systems.cc b/media/base/key_systems.cc
index 4567bf4c614a12bb8d46c1f758f44e302c5434ca..02d4b698701c00a8f79fece072e4332a0036f164 100644
--- a/media/base/key_systems.cc
+++ b/media/base/key_systems.cc
@@ -418,6 +418,9 @@ void KeySystemsImpl::AddSupportedKeySystems(
               properties->GetPepperType().empty());
     if (!properties->GetPepperType().empty())
       can_block = true;
+#elif defined(OS_ANDROID)
+    if (IsExternalClearKey(properties->GetKeySystemName()))
+      can_block = true;

[ddorwin, 2016/09/14 01:06:27]

Please add a comment. Maybe above with the general description.
We may also want to note that this is only a policy check and not a security
check since AesDecryptor runs in a different process, albeit the trusted browser
process.

[xhwang, 2016/09/16 18:50:17]

Done.

 #endif
     if (!can_block) {
       DCHECK(properties->GetDistinctiveIdentifierSupport() ==