Convert installer_util_unittests to run exclusively on Swarming

testing/buildbot/chromium.win.json

Index: testing/buildbot/chromium.win.json
diff --git a/testing/buildbot/chromium.win.json b/testing/buildbot/chromium.win.json
index 51f6c7e9c914b03225d633a55cf1e0f93b567a0c..4bbee12577efeae40fea81887d7523155533b1ed 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -138,6 +138,9 @@
         "test": "gpu_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "installer_util_unittests"
       },
       {
@@ -457,6 +460,9 @@
         "test": "gpu_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "installer_util_unittests"
       },
       {
@@ -908,6 +914,9 @@
         "test": "gpu_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "installer_util_unittests"
       },
       {
@@ -1225,6 +1234,9 @@
         "test": "gpu_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "installer_util_unittests"
       },
       {
@@ -1707,6 +1719,9 @@
         "test": "gpu_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "installer_util_unittests"
       },
       {