Fix generation of java enums

Fix generation of java enums

java_cpp_enum.gypi was creating all enums in the same root folder and
then adding that folder to its dependents generated_src_dirs. This has
two issues: first, incremental builds will include stale files when
things are moved/renamed/etc. second, all libraries that depend on such
an enum target will actually compile and include all the enum targets
(and in fact may even include different versions of one enum in
 different libraries).

This change just makes each such target use its own unique directory
(this will still have the stale enum issue when renaming an enum if the
 target name doesn't change, but that is very rare).

The GN version already used unique directories.

TBR=mkosiba

Committed: https://crrev.com/e98bcec0ee81f43526ad06a2e27a1cdc3ef7f190
Cr-Commit-Position: refs/heads/master@{#295595}

[cjhopman, 2014-09-18 17:41:15]

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

[cjhopman, 2014-09-18 17:41:15]

tedchoc: *

[Ted C, 2014-09-18 17:44:41]

lgtm

[cjhopman, 2014-09-18 17:57:50]

The CQ bit was checked by cjhopman@chromium.org

[commit-bot: I haz the power, 2014-09-18 17:58:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/578363002/1

[commit-bot: I haz the power, 2014-09-18 18:34:20]

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

[commit-bot: I haz the power, 2014-09-18 18:34:21]

Try jobs failed on following builders:
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)

[cjhopman, 2014-09-18 20:33:27]

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

[cjhopman, 2014-09-18 20:33:27]

mkosiba TBRed for android_webview/

[cjhopman, 2014-09-18 20:33:47]

The CQ bit was checked by cjhopman@chromium.org

[commit-bot: I haz the power, 2014-09-18 20:35:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/578363002/20001

[commit-bot: I haz the power, 2014-09-18 23:20:43]

Committed patchset #2 (id:20001) as 964bbc7f4f845d3928039e92378586a50b25338d

[commit-bot: I haz the power, 2014-09-18 23:21:24]

Patchset 2 (id:??) landed as
https://crrev.com/e98bcec0ee81f43526ad06a2e27a1cdc3ef7f190
Cr-Commit-Position: refs/heads/master@{#295595}

[mkosiba (inactive), 2014-09-19 12:46:52]

thanks!