Create blink_headers target for header-only dependencies

public/blink.gyp

Index: public/blink.gyp
diff --git a/public/blink.gyp b/public/blink.gyp
index ab7b7397c33ef274c1cb5c0d094073cfbfc86ccc..740d47401603b0dadae86d01e3f5fb9f54666a41 100644
--- a/public/blink.gyp
+++ b/public/blink.gyp
@@ -39,6 +39,7 @@
                 '../Source/web/web.gyp:blink_web',
                 '../Source/platform/blink_platform.gyp:blink_platform',
                 'blink_minimal',
+                'blink_headers',
             ],
             'export_dependent_settings': [
                 '../Source/web/web.gyp:blink_web',
@@ -47,6 +48,16 @@
             ],
         },
         {
+          # Depend on this target to use public blink API headers for things
+          # like enums and public structures without actually linking against any Blink
+          # libraries.
+          'target_name': 'blink_headers',
+          'type': 'none',
+          'direct_dependent_settings': {
+            'include_dirs': [ '..' ],
+          },
+        },
+        {
             # This target provides a minimal set of Blink APIs such as WebString to use in
             # places that cannot link against the full Blink library.
             # FIXME: We really shouldn't have this at all and should instead remove all uses