GitLab

For some reason, edit URL can be null in some entries, which
causes a crash.

Along the way, make |callback| parameter of DriveFilesystemInterface::Remove()
mandatory. The only caller in gdata_file_system_proxy.cc passes a non-null
callback.

BUG=144993
TEST=remove operation works as before


Review URL: https://chromiumcodereview.appspot.com/10880075

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153603 0039d316-1c4b-4281-b951-d872f2087c98