Fix order of includes in base_nacl.gyp

GYP wasn't generating correct list of dependencies when base.gypi was
included after untrusted.gypi. As result libbase_nacl.a wasn't always
rebuilt when the sources it depends on were changed.

BUG=461422

Review URL: https://codereview.chromium.org/976863002

Cr-Commit-Position: refs/heads/master@{#319092}

base/base_nacl.gyp

@@ -7,8 +7,12 @@
     'chromium_code': 1,
   },
   'includes': [
-    '../build/common_untrusted.gypi',
+    # base.gypi must be included before common_untrusted.gypi.
+    #
+    # TODO(sergeyu): Replace the target_defaults magic in base.gypi with a
+    # sources variables lists. That way order of includes will not matter.
     'base.gypi',
+    '../build/common_untrusted.gypi',
   ],
   'conditions': [
     ['disable_nacl==0 and disable_nacl_untrusted==0', {