Fix //content/plugin ax_enums gn build flake

Fix //content/plugin ax_enums gn build flake

Flake observerd with target_os="android" and enable_plugins=true:
//content/plugin/plugin_thread.cc ends up including the generated
ax_enums header so make it depend on it.

BUG=

Committed: https://crrev.com/d050925ac8f0324186269b1f10c0a8a9d24fab40
Cr-Commit-Position: refs/heads/master@{#348918}

[tsniatowski, 2015-09-15 06:33:33]

tsniatowski@opera.com changed reviewers:
+ ananta@chromium.org, jam@chromium.org
- jamesr@chromium.org

[tsniatowski, 2015-09-15 06:35:20]

PTAL. Either this dep, or a direct dep on //ui/accessibility:ax_gen fixes the
flake.

[jam, 2015-09-15 16:28:28]

lgtm

[tsniatowski, 2015-09-15 16:35:14]

The CQ bit was checked by tsniatowski@opera.com

[commit-bot: I haz the power, 2015-09-15 16:35:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1343883003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1343883003/1

[commit-bot: I haz the power, 2015-09-15 17:07:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-15 17:08:23]

Patchset 1 (id:??) landed as
https://crrev.com/d050925ac8f0324186269b1f10c0a8a9d24fab40
Cr-Commit-Position: refs/heads/master@{#348918}

[Devlin, 2015-09-15 17:48:02]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1339173003/ by rdevlin.cronin@chromium.org.

The reason for reverting is: This broke Win x64 GN builds:

ERROR Dependency cycle:
  //content:content ->
  //content/public/plugin:plugin_sources ->
  //content/plugin:plugin ->
  //content/public/common:common ->
  //content:content.

[tsniatowski, 2015-09-15 18:15:13]

Patchset #2 (id:20001) has been deleted

[tsniatowski, 2015-09-15 18:16:28]

On 2015/09/15 17:48:02, Devlin wrote:
> A revert of this CL (patchset #1 id:1) has been created in
> https://codereview.chromium.org/1339173003/ by
mailto:rdevlin.cronin@chromium.org.
> 
> The reason for reverting is: This broke Win x64 GN builds:
> 
> ERROR Dependency cycle:
>   //content:content ->
>   //content/public/plugin:plugin_sources ->
>   //content/plugin:plugin ->
>   //content/public/common:common ->
>   //content:content.

broke component build in general; fix in
https://codereview.chromium.org/1344883002

[commit-bot: I haz the power, 2015-09-23 12:46:16]

Patchset 1 (id:??) landed as
https://crrev.com/d050925ac8f0324186269b1f10c0a8a9d24fab40
Cr-Commit-Position: refs/heads/master@{#348918}