Fix Moz2D build

BUG=skia:2221
R=george@mozilla.com, reed@google.com

Author: borenet@google.com

Review URL: https://codereview.chromium.org/277593003

git-svn-id: http://skia.googlecode.com/svn/trunk@14647 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/common_variables.gypi b/gyp/common_variables.gypi
index 2add2ee..b6d4e76 100644
--- a/gyp/common_variables.gypi
+++ b/gyp/common_variables.gypi
@@ -219,6 +219,7 @@
     'skia_win_debuggers_path%': '<(skia_win_debuggers_path)',
     'skia_run_pdfviewer_in_gm%': 0,
     'skia_disable_inlining%': 0,
+    'skia_moz2d%': 0,
 
     # These are referenced by our .gypi files that list files (e.g. core.gypi)
     #