Adding support for service account credentials.

- Tested end to end with a JSON key I generated for my account using the
fetch_oauth2 binary.
- The same fetch_oauth2 binary can get a token from the GCE metadata service on a VM in cloud.
	Change on 2014/12/19 by jboeuf <jboeuf@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82548689
diff --git a/build.json b/build.json
index dc64378..50f3ca3 100644
--- a/build.json
+++ b/build.json
@@ -1088,6 +1088,18 @@
       ]
     },
     {
+      "name": "grpc_fetch_oauth2",
+      "build": "tool",
+      "src": [
+        "test/core/security/fetch_oauth2.c"
+      ],
+      "deps": [
+        "grpc_test_util",
+        "grpc",
+        "gpr"
+      ]
+    },
+    {
       "name": "grpc_base64_test",
       "build": "test",
       "src": [