Use swarming in builder for goma staging server

Goma gce staging bots on win fails on content_unittest.
I'm suspecting it is due to inappropriate setting of vm.
Let me enable swarming for those bots to pass test.

Bug: 687037
Change-Id: Ib89cb0716ca26a69392471d5c77e8d4a12e640cc
Reviewed-on: https://chromium-review.googlesource.com/721224Reviewed-by: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@google.com>
Cr-Commit-Position: refs/heads/master@{#509658}

testing/buildbot/chromium.goma.json

@@ -2,36 +2,134 @@
   "Chromium Linux Goma GCE Staging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "Chromium Linux Goma Staging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "Chromium Mac Goma GCE Staging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "Chromium Mac Goma Staging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "CrWinClangGomaGCEStaging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "CrWinGomaGCEStaging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   },
   "CrWinGomaStaging": {
     "additional_compile_targets": [
       "all"
+    ],
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_unittests"
+      }
     ]
   }
 }