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.

Review URL: https://codereview.chromium.org/927363005

Cr-Commit-Position: refs/heads/master@{#316874}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 01a3a6c..cac0942 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -697,6 +697,8 @@
     "test/tiled_layer_test_common.h",
   ]
 
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+
   include_dirs = [
     ".",
     "test",