Make components_browsertests swarmable and add to main waterfall.

testing/buildbot/chromium.mac.json

 {
   "Mac10.6 Tests": {
     "gtest_tests": [
       {
         "test": "accessibility_unittests",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
@@ skipping 13 matching lines @@
         "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 10
         }
       },
       "cacheinvalidation_unittests",
       "cast_unittests",
       "cc_unittests",
       "chromedriver_unittests",
       {
+        "test": "components_browsertests",
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        }
+      },
+      {
         "test": "components_unittests",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
         "test": "content_browsertests",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
@@ skipping 506 matching lines @@
         "name": "telemetry_perf_unittests",
         "script": "telemetry_perf_unittests.py"
       },
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
       }
     ]
   }
 }