Fix a bug in web_drag_dest_mac_unittest.mm.

Fix a bug in web_drag_dest_mac_unittest.mm.

The test puts a string representation of a file path into PasteBoard, and then
extracts the string again. The logic that extracts the string first converts
the string into a file URL. The implementation for that logic in CoreFoundation
has different behavior depending on whether Chrome is linked against an OSX
10.9+ SDK. The expectation of the test should compare the string extracted from
PasteBoard against the initial string converted into an NSURL, and then back
into a string.

BUG=484203
Committed: https://crrev.com/cf97bbac4cd96988c47b3cbee228d1c11a6ec9f4
Cr-Commit-Position: refs/heads/master@{#328791}

[erikchen, 2015-05-06 23:54:15]

erikchen@chromium.org changed reviewers:
+ avi@chromium.org

[erikchen, 2015-05-06 23:54:16]

avi: Please review.

[Avi (use Gerrit), 2015-05-07 03:31:10]

lgtm

I'm cool with this.

[erikchen, 2015-05-07 17:24:52]

The CQ bit was checked by erikchen@chromium.org

[commit-bot: I haz the power, 2015-05-07 17:25:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1128173004/20001

[commit-bot: I haz the power, 2015-05-07 17:43:49]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-07 17:45:24]

Patchset 2 (id:??) landed as
https://crrev.com/cf97bbac4cd96988c47b3cbee228d1c11a6ec9f4
Cr-Commit-Position: refs/heads/master@{#328791}