Update existing uses of /wd4267 to use the GN config

extensions/browser/BUILD.gn

Index: extensions/browser/BUILD.gn
diff --git a/extensions/browser/BUILD.gn b/extensions/browser/BUILD.gn
index a2b49b80ef8cb18e8e08b93d432ce457a78555e5..465945751d430d27f58ebef9cedd050bc19ec678 100644
--- a/extensions/browser/BUILD.gn
+++ b/extensions/browser/BUILD.gn
@@ -30,6 +30,9 @@ source_set("browser") {
     "//third_party/re2",
   ]
 
+  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+
   if (enable_extensions) {
     # Includes all API implementations and the ExtensionsApiClient
     # interface. Moving an API from src/chrome to src/extensions implies
@@ -97,8 +100,4 @@ source_set("browser") {
       }
     }
   }
-
-  if (is_win) {
-    cflags = [ "/wd4267" ]  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-  }
 }