Enable cc_perftests on "Linux Perf (3)".

testing/buildbot/chromium.perf.json

 {
+  "Linux Perf (3)": {
+    "scripts": [
+      {
+        "name": "cc_perftests",
+        "script": "gtest_perf_test.py",
+        "args": ["cc_perftests", "--test-launcher-print-test-stdio=always"]
+      }
+    ]
+  },
   "Android Nexus4 Perf": {
     "scripts": [
       {
         "name": "host_info",
         "script": "host_info.py"
       }
     ]
   },
   "Android Nexus5 Perf": {
     "scripts": [
@@ skipping 29 matching lines @@
   },
   "Mac 10.8 Perf (1)": {
     "scripts": [
     ]
   },
   "Mac 10.9 Perf (1)": {
     "scripts": [
     ]
   }
 }