win: Disable warning 4275, make NON_EXPORTED_BASE a no-op.

This points out a potential (but rare) problem with referencing static
fields of a non-exported base, through the base's non-exported inline
functions, or directly. The warning is subtle enough that people just
suppressed it when they saw it, so it's not worth it.

Bug: 752837
Change-Id: Ia9b8307f77e155416bdfdad28ff33df3081a434b
Reviewed-on: https://chromium-review.googlesource.com/603773
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#492411}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4b77236a76acca2eb885b5021a0ede75efe29962

config/compiler/BUILD.gn

@@ -1003,6 +1003,13 @@ config("default_warnings") {
       # This is necessary for the shared library build.
       "/wd4251",
 
+      # C4275:  non dll-interface class used as base for dll-interface class
+      # This points out a potential (but rare) problem with referencing static
+      # fields of a non-exported base, through the base's non-exported inline
+      # functions, or directly. The warning is subtle enough that people just
+      # suppressed it when they saw it, so it's not worth it.
+      "/wd4275",
+
       # C4312 is a VS 2015 64-bit warning for integer to larger pointer.
       # TODO(brucedawson): fix warnings, crbug.com/554200
       "/wd4312",