Work on GN Win64 build.

Work on GN Win64 build.

Adds a new config to disable size_t -> int truncations and use it in various places where the x64 Windows build currently gives warnings.

This covers Chrome (except for Blink which has a separate patch) and the tests.

We should do a second pass to replace the existing instances of /wd4267 with this config.

Committed: https://crrev.com/1deb76bc64a51808cd3df93d8166f223241487fe
Cr-Commit-Position: refs/heads/master@{#316874}

[brettw, 2015-02-18 00:28:54]

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

[Dirk Pranke, 2015-02-18 01:31:17]

lgtm.

+rockot, who was hitting this exact thing on a patch earlier today and to whom I
suggested use //build/compiler/no_chromium_code instead.

One nit, though: I personally would've called this "no_size_t_to_int_warning"
with an underscore in the size_t. I don't feel strongly enough about this to not
approve, but if you were at all on the fence, consider this a vote for an
underscore.

[brettw, 2015-02-18 17:40:31]

Okay, I was on the fence about the underscore so I added it.

[brettw, 2015-02-18 17:40:35]

New patchsets have been uploaded after l-g-t-m from dpranke@chromium.org

[brettw, 2015-02-18 17:40:43]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-02-18 17:41:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/927363005/20001

[commit-bot: I haz the power, 2015-02-18 19:28:36]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-18 19:29:35]

Patchset 2 (id:??) landed as
https://crrev.com/1deb76bc64a51808cd3df93d8166f223241487fe
Cr-Commit-Position: refs/heads/master@{#316874}