Update third_party/webdriver/pylib to r18456 and delete test_data

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
 #   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 # where <gcliendir> is the absolute path to the directory containing the
 # .gclient file (the parent of "src").
 #
@@ skipping 192 matching lines @@
   "src/third_party/bidichecker":
     (Var("googlecode_url") % "bidichecker") + "/trunk/lib@4",
 
   "src/third_party/webgl/src":
     Var("chromium_git") +
     "/external/khronosgroup/webgl.git@7c8cb656a753b6237e50c546c31ad826373abf04",
 
   "src/third_party/swig/Lib":
     "/trunk/deps/third_party/swig/Lib@" + Var("swig_revision"),
 
-  # Make sure you update the two functional.DEPS and webdriver.DEPS too.
   "src/third_party/webdriver/pylib":
-    (Var("googlecode_url") % "selenium") + "/trunk/py@18337",
+    (Var("googlecode_url") % "selenium") + "/trunk/py@18456",
 
   "src/third_party/libvpx":
     "/trunk/deps/third_party/libvpx@" +
     Var("libvpx_revision"),
 
   "src/third_party/ffmpeg":
     Var("chromium_git") +
     "/chromium/third_party/ffmpeg.git@e2a05d173d49547ed8aa5edc0209941a8941f450",
 
   "src/third_party/libjingle/source/talk":
@@ skipping 579 matching lines @@
                 "src/third_party/apache-win32",
     ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "name": "gyp",
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
 ]