win: /utf-8 for all code

Previously enabled for chromium_code, can now be turned on everywhere.

BUG=454858,637203, 671021

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win_optional_gpu_tests_rel
Committed: https://crrev.com/a53f3c3734ad9ee4322f6a9a60eede7f6b04530f
Cr-Commit-Position: refs/heads/master@{#436189}

Review-Url: https://codereview.chromium.org/2543743002
Cr-Commit-Position: refs/heads/master@{#438029}

build/config/compiler/BUILD.gn

@@ -839,6 +839,11 @@ config("default_warnings") {
       cflags += [ "/WX" ]
     }
 
+    cflags += [
+      # Assume UTF-8 by default to avoid code page dependencies.
+      "/utf-8",
+    ]
+
     cflags += [
       # Warnings permanently disabled:
 
@@ -1070,9 +1075,6 @@ config("default_warnings") {
 config("chromium_code") {
   if (is_win) {
     cflags = [ "/W4" ]  # Warning level 4.
-
-    # Assume UTF-8 by default to avoid code page dependencies.
-    cflags += [ "/utf-8" ]
   } else {
     cflags = [ "-Wall" ]
     if (treat_warnings_as_errors) {