Move benchmark buck file into benchmark directory

Summary: buck rules are not meant to be in the root buck file but instead next to source files. This diff moves benchmark rule into benchmark folder.

Reviewed By: lucasr

Differential Revision: D3992992

fbshipit-source-id: 34782ff73bbd5b799d83d0f01b553bfab928f1df

CSSLAYOUT_DEFS

@@ -9,6 +9,9 @@ GTEST_TARGET = '//lib/gtest:gtest'
 GTEST_DL_URL = 'https://github.com/google/googletest/archive/release-1.7.0.zip'
 JNI_DEPS = ['//lib/fb:fbjni']
 
+def csslayout_dep(dep):
+  return '//' + dep
+
 class allow_unsafe_import:
     def __enter__(self):
         pass