Move wtf_unittests to platform/wtf/.

testing/buildbot/gn_isolate_map.pyl

 ## Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This is a .pyl, or "Python Literal", file. You can treat it just like a
 # .json file, with the following exceptions:
 # * all keys must be quoted (use single quotes, please);
 # * comments are allowed, using '#' syntax; and
 # * trailing commas are allowed.
 
@@ skipping 1077 matching lines @@
   },
   "webkit_unit_tests": {
     "label": "//third_party/WebKit/Source/web:webkit_unit_tests",
     "type": "console_test_launcher",
   },
   "wm_unittests": {
     "label": "//ui/wm:wm_unittests",
     "type": "windowed_test_launcher",
   },
   "wtf_unittests": {
-    "label": "//third_party/WebKit/Source/wtf:wtf_unittests",
+    "label": "//third_party/WebKit/Source/platform/wtf:wtf_unittests",
     "type": "console_test_launcher",
   },
 }