Convert chromedriver_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 53dbd2cb9467838e7d4e761ab5dad082a9e13879..8be1b1fdc2c89a50dd8346a26e7561a0cada582f 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -54,6 +54,9 @@
         "test": "chrome_elf_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "chromedriver_unittests"
       },
       {
@@ -349,6 +352,9 @@
         "test": "chrome_elf_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "chromedriver_unittests"
       },
       {
@@ -784,6 +790,9 @@
         "test": "chrome_elf_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "chromedriver_unittests"
       },
       {
@@ -1108,6 +1117,9 @@
         "test": "chrome_elf_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "chromedriver_unittests"
       },
       {
@@ -1554,6 +1566,9 @@
         "test": "chrome_elf_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "chromedriver_unittests"
       },
       {