Convert compositor_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 b0b81434346c28dd508a2b84245229df73a15641..90521601e9a44bbbf3632169c8e638cb9ac4925e 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -63,6 +63,9 @@
         "test": "components_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "compositor_unittests"
       },
       {
@@ -358,6 +361,9 @@
         "test": "components_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "compositor_unittests"
       },
       {
@@ -787,6 +793,9 @@
         "test": "components_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "compositor_unittests"
       },
       {
@@ -1099,6 +1108,9 @@
         "test": "components_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "compositor_unittests"
       },
       {
@@ -1548,6 +1560,9 @@
         "test": "components_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "compositor_unittests"
       },
       {