Fix various flags in the Win64 GN build

Fix various flags in the Win64 GN build

-disable chromium_code for third_party/zlib
- suppress a few size_t -> int conversion warnings
- suppress /wd4121 (structure padding) by default;
  was suppressed in GYP but not GN.

Also disable ffmpeg, which doesn't work in the 64-bit build yet.

R=scottmg@chromium.org
TBR=brettw@chromium.org
BUG=432375, 167187
Committed: https://crrev.com/de7d0dc942b1e296a0e9bd667f020ffd486cc32e
Cr-Commit-Position: refs/heads/master@{#304542}

[scottmg, 2014-11-17 23:25:48]

lgtm

[Dirk Pranke, 2014-11-18 00:59:39]

Please take another look? This has a couple additional changes, so I've updated
the description.

[scottmg, 2014-11-18 01:01:13]

https://codereview.chromium.org/737633002/diff/20001/build/config/compiler/BU...
File build/config/compiler/BUILD.gn (right):

https://codereview.chromium.org/737633002/diff/20001/build/config/compiler/BU...
build/config/compiler/BUILD.gn:693: "/wd4121",  # Alignment of a member was
sensitive to packing.
I don't see this one in gyp?

[scottmg, 2014-11-18 01:01:43]

sorry, just missed it. still lgtm.

[Dirk Pranke, 2014-11-18 01:07:41]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-11-18 01:08:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/737633002/20001

[commit-bot: I haz the power, 2014-11-18 01:13:05]

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

[commit-bot: I haz the power, 2014-11-18 01:13:06]

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

[Dirk Pranke, 2014-11-18 01:29:14]

dpranke@chromium.org changed reviewers:
+ brettw@chromium.org

[Dirk Pranke, 2014-11-18 01:29:18]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-11-18 01:30:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/737633002/20001

[commit-bot: I haz the power, 2014-11-18 01:34:57]

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

[commit-bot: I haz the power, 2014-11-18 01:34:59]

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

[Dirk Pranke, 2014-11-18 01:42:49]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-11-18 01:43:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/737633002/20001

[commit-bot: I haz the power, 2014-11-18 01:55:04]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-18 01:55:37]

Patchset 2 (id:??) landed as
https://crrev.com/de7d0dc942b1e296a0e9bd667f020ffd486cc32e
Cr-Commit-Position: refs/heads/master@{#304542}