This change enables tcmalloc on Win64

BUG=177300


Review URL: https://chromiumcodereview.appspot.com/12324020

git-svn-id: http://src.chromium.org/svn/trunk/src/build@184292 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -2243,10 +2243,6 @@
               ['<(windows_sdk_path)/Lib/win8/um/x64'],
           },
         },
-        'defines': [
-          # Not sure if tcmalloc works on 64-bit Windows.
-          'NO_TCMALLOC',
-        ],
       },
       'Debug_Base': {
         'abstract': 1,