Convert printing_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 3593de057889285bb53407ee58a0e726f419635b..f41ddf620b754cec991a8155b976363341c2684f 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -181,6 +181,9 @@
         "test": "ppapi_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "printing_unittests"
       },
       {
@@ -458,6 +461,9 @@
         "test": "ppapi_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "printing_unittests"
       },
       {
@@ -854,6 +860,9 @@
         "test": "ppapi_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "printing_unittests"
       },
       {
@@ -1110,6 +1119,9 @@
         "test": "ppapi_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "printing_unittests"
       },
       {
@@ -1525,6 +1537,9 @@
         "test": "ppapi_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "printing_unittests"
       },
       {