Make components_browsertests swarmable and add to main waterfall.

testing/buildbot/chromium.linux.json

 {
   "Linux Tests": {
     "gtest_tests": [
       {
         "test": "accessibility_unittests",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
@@ skipping 16 matching lines @@
         "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 5
         }
       },
       "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
         }
       },
       "compositor_unittests",
       {
         "test": "content_browsertests",
         "swarming": {
           "can_use_on_swarming_builders": true
@@ skipping 451 matching lines @@
       "nacl_loader_unittests",
       "sandbox_linux_unittests",
       "sql_unittests",
       "sync_unit_tests",
       "ui_base_unittests",
       "unit_tests",
       "skia_unittests"
     ]
   }
 }