Convert gl_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..ae17e549418c6caba0aa451d202d8e15a5db43ad 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -120,6 +120,9 @@
         "test": "gfx_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "gl_unittests"
       },
       {
@@ -421,6 +424,9 @@
         "test": "gfx_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "gl_unittests"
       },
       {
@@ -850,6 +856,9 @@
         "test": "gfx_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "gl_unittests"
       },
       {
@@ -1605,6 +1614,9 @@
         "test": "gfx_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "gl_unittests"
       },
       {