Add storage_unittests to buildbots.

testing/buildbot/chromium_memory_trybot.json

 {
   "gtest_tests": [
     "accessibility_unittests",
     {
       "swarming": {
         "can_use_on_swarming_builders": true
       },
       "test": "base_unittests"
     },
     {
@@ skipping 113 matching lines @@
     "printing_unittests",
     "remoting_unittests",
     {
       "platforms": [
         "linux"
       ],
       "test": "sandbox_linux_unittests"
     },
     "skia_unittests",
     "sql_unittests",
+    {
+      "swarming": {
+        "can_use_on_swarming_builders": true
+      },
+      "test": "storage_unittests"
+    },
     "ui_base_unittests",
     {
       "swarming": {
         "can_use_on_swarming_builders": true,
         "shards": 2
       },
       "test": "unit_tests"
     },
     "url_unittests"
   ]
 }