[gcc 4.x] Fix the build failure due to -Werror=char-subscripts

[gcc 4.x] Fix the build failure due to -Werror=char-subscripts

Make the 'char' to 'unsigned char' to fix the following build failure.

device/hid/hid_connection_unittest.cc: In member function ‘virtual void device::HidConnectionTest_ReadWrite_Test::TestBody()’:
device/hid/hid_connection_unittest.cc:166:23: error: array subscript has type ‘char’ [-Werror=char-subscripts]
       buffer->data()[j] = i + j - 1;
                       ^
device/hid/hid_connection_unittest.cc:179:285: error: array subscript has type ‘char’ [-Werror=char-subscripts]
       ASSERT_EQ(i + j - 1, read_callback.buffer()->data()[j])

Committed: https://crrev.com/3a9e7ea06f717789c3304ad4fc085e8f621a8088
Cr-Commit-Position: refs/heads/master@{#300238}

[vivekg, 2014-10-20 03:45:43]

vivekg@chromium.org changed reviewers:
+ pkasting@chromium.org, reillyg@chromium.org

[vivekg, 2014-10-20 03:45:43]

Please take a look, thanks.

[Reilly Grant (use Gerrit), 2014-10-20 04:12:01]

lgtm

[vivekg, 2014-10-20 04:50:36]

The CQ bit was checked by vivekg@chromium.org

[commit-bot: I haz the power, 2014-10-20 04:51:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/664983002/1

[commit-bot: I haz the power, 2014-10-20 09:36:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-20 09:37:08]

Patchset 1 (id:??) landed as
https://crrev.com/3a9e7ea06f717789c3304ad4fc085e8f621a8088
Cr-Commit-Position: refs/heads/master@{#300238}