[fsp] Fix incorrect handling of file system URLs when containing a %.

Mount point names can (and in case of File System Provider API often do) the %
character, in order to create a safe mount point name from an arbitrary file
system id, which can be any string, and often is a file name path. Such path
may contain /, which have to be escaped, since the mount point name must not
contain that character.

However, GetExternalFileSystemRootURIString() wasn't properly escaping the %
character, what caused treating it later as an encoding sequence of an url.

TEST=Tested manually with a file systems containing % in the mount point name.
BUG=248427

Review URL: https://codereview.chromium.org/312283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276002 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed