Fix java_cpp_enum.gypi so that source_file changes will rebuild dependencies.

Fix java_cpp_enum.gypi so that source_file changes will rebuild dependencies.

As a result, if a generated .java class had to be added to a .jar file, the
java class would be rebuilt but the jar file would not be updated.

This has caused landmines in the past:
https://codereview.chromium.org/899403002

It is fixing the underlying issue blocking this:
https://codereview.chromium.org/1003143002

BUG=457038
Committed: https://crrev.com/86c3b5b8bf1aa48335f8213bcaa85ce45748a8a4
Cr-Commit-Position: refs/heads/master@{#322717}

[mlamouri (slow - plz ping), 2015-03-28 20:24:54]

mlamouri@chromium.org changed reviewers:
+ cjhopman@chromium.org, klundberg@chromium.org, thakis@chromium.org

[mlamouri (slow - plz ping), 2015-03-28 20:24:54]

mlamouri@chromium.org changed required reviewers:
+ klundberg@chromium.org

[mlamouri (slow - plz ping), 2015-03-28 20:24:54]

cjhopman@, could you review this change as a de-facto owner of this file?
klundberg@, could you review this change as an OWNER of build/android/?
thakis@, FYI

Thanks :)

[mlamouri (slow - plz ping), 2015-03-28 20:25:44]

On 2015/03/28 at 20:24:54, Mounir Lamouri wrote:
> cjhopman@, could you review this change as a de-facto owner of this file?
> klundberg@, could you review this change as an OWNER of build/android/?
> thakis@, FYI
> 
> Thanks :)

-klundberg@, because cjhopman@ is build/ OWNERS.

[mlamouri (slow - plz ping), 2015-03-28 20:25:54]

mlamouri@chromium.org changed reviewers:
- klundberg@chromium.org

[mlamouri (slow - plz ping), 2015-03-28 20:25:54]

mlamouri@chromium.org changed required reviewers:
+ cjhopman@chromium.org
- klundberg@chromium.org

[cjhopman, 2015-03-29 01:46:02]

lgtm

[mlamouri (slow - plz ping), 2015-03-29 11:13:59]

The CQ bit was checked by mlamouri@chromium.org

[commit-bot: I haz the power, 2015-03-29 11:14:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1040643003/1

[commit-bot: I haz the power, 2015-03-29 11:16:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-29 11:18:35]

Patchset 1 (id:??) landed as
https://crrev.com/86c3b5b8bf1aa48335f8213bcaa85ce45748a8a4
Cr-Commit-Position: refs/heads/master@{#322717}

[Nico, 2015-03-30 19:03:22]

lgtm, thanks for the fix! 

(I think this still isn't quite right if an enum is removed from a header. In
that case, the old generated .java file will stay around in the build dir and
still end up in the jar. This would probably be easier to get right if the
outputs were explicitly listed in the gyp file, then they could be explicitly
passed to the step that compiles .java files to .jar files – kind of like the gn
build does this.)