Disable webkit_unit_tests on 'ThinLTO Linux ToT'.

testing/buildbot/chromium.fyi.json

 {
   "Android Asan Builder Tests (dbg)": {
     "gtest_tests": [
       {
         "args": [
           "--tool=asan"
         ],
         "swarming": {
           "can_use_on_swarming_builders": false
         },
@@ skipping 11874 matching lines @@
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "views_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "webkit_unit_tests"
-      },
-      {
-        "swarming": {
-          "can_use_on_swarming_builders": true
-        },
         "test": "wm_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "wtf_unittests"
       }
     ]
   },
@@ skipping 564 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "views_unittests"
       }
     ]
   }
 }