Allow read access on a root directory of IsolatedFileSystem

Allow read access on a root directory of IsolatedFileSystem

Since r124366 we started checking file permission against
ChildProcessSecurityPolicy on each operation but the current
code prohibits read access on a root directory of IsolatedFileSystem,
since the root directory in IsolatedFileSystem is purely virtual and
has no associated platform path (to check the permission).

BUG=none
TEST=manual

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=138073

[kinuko, 2012-05-18 07:03:02]

(Gush I haven't published this...) Can you take a look?Thanks!

Additional note: why we may want this to work?
If we support this one can simply copy all the dropped files/directories from
isolated to temp/perm by calling copyTo on the root directory.  We *could*
return error if we don't want to support this, but it sounds neat.

[tzik, 2012-05-18 07:21:20]

lgtm

[ericu, 2012-05-21 21:36:29]

LGTM.

Calling copyTo on the root would then create a new directory containing all the
root contents?  That seems perfectly reasonable.

Example:

dragging /isolated/id/foo/bar, /isolated/id/foo/bas, /isolated/id/bling
isolated_root.copyTo(/temporary/hoge)

Now you have:

/temporary/hoge/foo/bar
/temporary/hoge/foo/bas
/temporary/hoge/bling