Add patch for WebKit after updating Chromium.

Including Assertions.h leads to __darwin_ssize_t being
defined inside namespace WebKit but not outside that namespace.
This is because certain headers will not be pulled in again
later on in the same compilation unit.

This patch has already been upstreamed,
and can be removed with the next Chromium update.

Change-Id: I302bbf779fcabb909a9ffda53d8b9fdccc87e248
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>