compositor_unittests target is unimplmented on Mac

printing/printing.gyp

Index: printing/printing.gyp
diff --git a/printing/printing.gyp b/printing/printing.gyp
index 34e3b4eb801060d705abefc7d3b1bc194ef31ba3..495fc73777e50da8c5bf8ebc41159b24483fe911 100644
--- a/printing/printing.gyp
+++ b/printing/printing.gyp
@@ -111,6 +111,14 @@
             ['exclude', 'metafile_skia_wrapper\\.(cc|h)$'],
           ],
         }],
+        # Mac-Aura does not support printing.
+        ['OS=="mac" and use_aura==1',{
+          'sources!': [
+            'printed_document_mac.cc',
+            'printing_context_mac.mm',
+            'printing_context_mac.h',
+          ],
+        }],
         ['OS=="mac" and use_aura==0',{
           'sources': [
             'printing_context_mac.mm',