[code coverage] Adding url_unittests to CI coverage builder.

R=liaoyuke,stgao,jbudorick

Change-Id: I1b9568f37d7ab6813095c1078fc8380fce231723
Reviewed-on: https://chromium-review.googlesource.com/c/1316654Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>
Commit-Queue: Shuotao Gao <stgao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605115}

testing/buildbot/chromium.fyi.json

@@ -5861,6 +5861,14 @@
           "shards": 2
         },
         "test": "base_unittests"
+      },
+      {
+        "isolate_coverage_data": true,
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "shards": 2
+        },
+        "test": "url_unittests"
       }
     ]
   },

testing/buildbot/test_suites.pyl

@@ -679,6 +679,11 @@
           'shards': 2,
         },
       },
+      'url_unittests': {
+        'swarming': {
+          'shards': 2,
+        },
+      },
     },
 
     'chromium_linux_scripts': {