Make a copy of webcore_test_database in content test data.

Apparently tryserver is not capable of doing tries with binary data so
we need to copy first then update the test.

This was discovered while doing https://codereview.chromium.org/403453002/.

BUG=338338
TEST=None
TBR=jam@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/405753003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284339 0039d316-1c4b-4281-b951-d872f2087c98

content/test/data/dom_storage/README.txt

+webcore_test_database.localstorage - This is a sample local storage database
+  generated by Chromium 17.0.963.38 beta (using the WebCore DOM Storage
+  backend). It is used in webkit/dom_storage/dom_storage_database_unittest.cc
+  to verify that the Chromium backend can read a WebCore generated database.