Add Test to make sure associated objects live/die with lifetime of UIView.

Summary: Wrote some tests to make sure the associated objects we use for layout live and die with the objects. This was worthwhile because it made me realize UIView+CSSLayout wasn't enabled to ARC. As a result, my tests were failing because they weren't explicitly deallocing nodes.

Reviewed By: rnystrom

Differential Revision: D4023324

fbshipit-source-id: 5356cf4f0522582d75f83b5eb2193d9bc8d63aee

uikit/CSSLayout/BUCK

@@ -7,8 +7,11 @@
 
 include_defs('//CSSLAYOUT_DEFS')
 
+UIKIT_CSSLAYOUT_COMPILER_FLAGS = ['-fobjc-arc']
+
 apple_library(
   name = 'CSSLayout',
+  compiler_flags = UIKIT_CSSLAYOUT_COMPILER_FLAGS,
   tests = [':CSSLayoutTests'],
   srcs = glob(['*.m']),
   exported_headers = glob(['*.h']),
@@ -24,6 +27,7 @@ apple_library(
 
 apple_test(
   name = 'CSSLayoutTests',
+  compiler_flags = UIKIT_CSSLAYOUT_COMPILER_FLAGS,
   info_plist = 'Tests/Info.plist',
   srcs = glob(['Tests/**/*.m']),
   frameworks = [