Repurpose Release_Developer BUILDTYPE and remove SK_DEVELOPER.

gyp/common.gypi

Index: gyp/common.gypi
diff --git a/gyp/common.gypi b/gyp/common.gypi
index ae6dd628cc2fb268e0aad9066b940f984a3bbf19..e0196cfd2af70c1d46d2fe8a10c4a92af0c63051 100644
--- a/gyp/common.gypi
+++ b/gyp/common.gypi
@@ -97,11 +97,11 @@
         # one makefile and allow someone to add SK_DEBUG etc for their own
         # debugging purposes.
         'configurations': {
-          'Debug':   { 'defines': [ 'SK_DEVELOPER=1' ] },
+          'Debug':   { 'defines': [ 'SK_DEBUG=1' ] },
           'Release': { 'defines': [ 'NDEBUG' ] },
           'Release_Developer': {
             'inherit_from': ['Release'],
-            'defines': [ 'SK_DEVELOPER=1' ],
+            'defines': [ 'SK_DEBUG=1' ],
           },
         },
       }],