Add a GN flag for the Windows multi-dll build.

Add a GN flag for the Windows multi-dll build.

The first pass of moving the other Chrome-specific build flags out of the root build config file and into the new one. This requires both ffmpeg and Blink changes to finish landing.

Originally landed as https://codereview.chromium.org/1120803003/
TBR=scottmg@chromium.org
TBR=ddorwin@chromium.org (widevine)
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:android_chromium_gn_compile_dbg,android_chromium_gn_compile_rel;tryserver.chromium.win:win8_chromium_gn_rel,win8_chromium_gn_dbg;tryserver.chromium.mac:mac_chromium_gn_rel,mac_chromium_gn_dbg

Committed: https://crrev.com/2b2364bb2c6fbb88e6a4550abeb9141bc7cb949c
Cr-Commit-Position: refs/heads/master@{#327998}

[brettw, 2015-05-01 16:08:32]

Original CL is in patch set 1.

[brettw, 2015-05-01 16:09:42]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-05-01 16:09:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123433002/20001

[commit-bot: I haz the power, 2015-05-01 16:57:14]

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

[commit-bot: I haz the power, 2015-05-01 16:57:15]

Try jobs failed on following builders:
  win8_chromium_gn_rel on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_gn_...)

[brettw, 2015-05-01 17:20:47]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-05-01 17:21:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123433002/40001

[ddorwin, 2015-05-01 17:41:14]

ddorwin@chromium.org changed reviewers:
+ ddorwin@chromium.org

[ddorwin, 2015-05-01 17:41:14]

third_party/widevine LGTM

[commit-bot: I haz the power, 2015-05-01 17:56:23]

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

[commit-bot: I haz the power, 2015-05-01 17:56:24]

Try jobs failed on following builders:
  win8_chromium_gn_rel on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_gn_...)

[brettw, 2015-05-01 18:18:44]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-05-01 18:18:44]

The patchset sent to the CQ was uploaded after l-g-t-m from ddorwin@chromium.org
Link to the patchset: https://codereview.chromium.org/1123433002/#ps60001
(title: " ")

[commit-bot: I haz the power, 2015-05-01 18:19:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123433002/60001

[commit-bot: I haz the power, 2015-05-01 19:12:47]

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

[commit-bot: I haz the power, 2015-05-01 19:12:48]

Try jobs failed on following builders:
  win8_chromium_gn_rel on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_gn_...)

[brettw, 2015-05-01 19:25:58]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-05-01 19:25:59]

The patchset sent to the CQ was uploaded after l-g-t-m from ddorwin@chromium.org
Link to the patchset: https://codereview.chromium.org/1123433002/#ps80001
(title: " ")

[commit-bot: I haz the power, 2015-05-01 19:27:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123433002/80001

[commit-bot: I haz the power, 2015-05-01 20:40:12]

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

[commit-bot: I haz the power, 2015-05-01 20:40:13]

Try jobs failed on following builders:
  win8_chromium_gn_rel on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_gn_...)

[brettw, 2015-05-01 21:29:39]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-05-01 21:29:39]

The patchset sent to the CQ was uploaded after l-g-t-m from ddorwin@chromium.org
Link to the patchset: https://codereview.chromium.org/1123433002/#ps100001
(title: " ")

[commit-bot: I haz the power, 2015-05-01 21:31:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123433002/100001

[commit-bot: I haz the power, 2015-05-01 22:36:36]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-05-01 22:37:30]

Patchset 6 (id:??) landed as
https://crrev.com/2b2364bb2c6fbb88e6a4550abeb9141bc7cb949c
Cr-Commit-Position: refs/heads/master@{#327998}