Fix invalid depfile generation in generate_split_manifest.py

Fix invalid depfile generation in generate_split_manifest.py

This caused ninja to crash for incremental builds of ChromeModern.apk

BUG=447152
Committed: https://crrev.com/afad5c2282c80622b28d112f757fe3d6c06dfa1a
Cr-Commit-Position: refs/heads/master@{#335060}

[agrieve, 2015-06-15 19:07:50]

agrieve@chromium.org changed reviewers:
+ cjhopman@chromium.org

[cjhopman, 2015-06-17 21:19:12]

lgtm

[agrieve, 2015-06-18 00:28:08]

The CQ bit was checked by agrieve@chromium.org

[commit-bot: I haz the power, 2015-06-18 00:30:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1187903003/1

[commit-bot: I haz the power, 2015-06-18 02:00:07]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-18 02:00:09]

Try jobs failed on following builders:
  win8_chromium_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_ng/...)

[agrieve, 2015-06-18 15:38:54]

The CQ bit was checked by agrieve@chromium.org

[commit-bot: I haz the power, 2015-06-18 15:39:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1187903003/1

[commit-bot: I haz the power, 2015-06-18 16:26:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-18 16:27:25]

Patchset 1 (id:??) landed as
https://crrev.com/afad5c2282c80622b28d112f757fe3d6c06dfa1a
Cr-Commit-Position: refs/heads/master@{#335060}