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/content/common/BUILD.gn b/content/common/BUILD.gn
index 6bf0f64..9ca66d24 100644
--- a/content/common/BUILD.gn
+++ b/content/common/BUILD.gn
@@ -130,7 +130,10 @@
                         ".",
                         "//content")
 
-  configs += [ "//content:content_implementation" ]
+  configs += [
+    "//content:content_implementation",
+    "//build/config/compiler:no_size_t_to_int_warning",
+  ]
 
   public_deps = [
     "//gpu/command_buffer/common",
@@ -453,6 +456,11 @@
       ]
     }
   }
+
+  if (is_win && cpu_arch == "x64") {
+    # TODO(jschuh): Remove this after crbug.com/173851 gets fixed.
+    cflags = [ "/bigobj" ]
+  }
 }
 
 mojom("mojo_bindings") {