vs2015: avoid narrowing warning in plugin_service_impl

vs2015: avoid narrowing warning in plugin_service_impl

[171->263/443 ~9] CXX obj\content\browser\content_browser.plugin_service_impl.obj
FAILED: ninja -t msvc -e environment.x86 -- "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\cl.exe" /nologo /showIncludes /FC @obj\content\browser\content_browser.plugin_service_impl.obj.rsp /c ..\..\content\browser\plugin_service_impl.cc /Foobj\content\browser\content_browser.plugin_service_impl.obj /Fdobj\content\content_browser.cc.pdb
d:\src\cr2\src\content\browser\plugin_service_impl.cc(842): error C2220: warning treated as error - no 'object' file generated
d:\src\cr2\src\content\browser\plugin_service_impl.cc(842): warning C4302: 'reinterpret_cast': truncation from 'HANDLE' to 'ATOM'

R=jam@chromium.org
BUG=440500
Committed: https://crrev.com/4800fc26e63ee53d9c1532e1519c738a85f34f86
Cr-Commit-Position: refs/heads/master@{#327403}

[scottmg, 2015-04-28 20:10:36]

scottmg@chromium.org changed reviewers:
+ jam@chromium.org

[scottmg, 2015-04-28 20:11:40]

The CQ bit was checked by scottmg@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-04-28 20:12:22]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1111913002/1

[commit-bot: I haz the power, 2015-04-28 21:26:32]

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

[commit-bot: I haz the power, 2015-04-28 21:26:33]

Dry run: This issue passed the CQ dry run.

[jam, 2015-04-29 00:24:52]

lgtm

[scottmg, 2015-04-29 00:29:12]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2015-04-29 00:29:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1111913002/1

[commit-bot: I haz the power, 2015-04-29 00:31:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-29 00:32:25]

Patchset 1 (id:??) landed as
https://crrev.com/4800fc26e63ee53d9c1532e1519c738a85f34f86
Cr-Commit-Position: refs/heads/master@{#327403}