Drive API: Generates randum boundary for multipart uploading.

Drive API: Generates randum boundary for multipart uploading.

Previously Drive API uses constant boundary for multipart uploading.  This CL
let the API generate a random boundary and ensure the boundary is not included
in the content part.

BUG=269922
TEST=None

Committed: https://crrev.com/9ae6ba6746014b5a9f9323be6bf7ef815903e5ab
Cr-Commit-Position: refs/heads/master@{#310689}

[hirono, 2015-01-09 01:09:10]

hirono@chromium.org changed reviewers:
+ kinaba@chromium.org

[hirono, 2015-01-09 01:09:11]

PTAL the CL? Thanks!

[kinaba, 2015-01-09 01:34:46]

lgtm

[hirono, 2015-01-09 01:39:21]

The CQ bit was checked by hirono@chromium.org

[hirono, 2015-01-09 01:39:26]

On 2015/01/09 01:34:46, kinaba wrote:
> lgtm

Thanks!

[commit-bot: I haz the power, 2015-01-09 01:40:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/805153006/20001

[commit-bot: I haz the power, 2015-01-09 02:52:01]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-09 02:53:25]

Patchset 2 (id:??) landed as
https://crrev.com/9ae6ba6746014b5a9f9323be6bf7ef815903e5ab
Cr-Commit-Position: refs/heads/master@{#310689}