ART: Add object-readbarrier-inl.h

Move some read-barrier code into a new header. This prunes the
include tree for the concurrent-copying collector. Clean up other
related includes.

Test: mmma art
Change-Id: I40ce4e74f2e5d4c692529ffb4df933230b6fd73e
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index c840e70..5136d7d 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -47,6 +47,7 @@
 #include "dex/verified_method.h"
 #include "driver/compiler_driver.h"
 #include "graph_visualizer.h"
+#include "intern_table.h"
 #include "intrinsics.h"
 #include "leb128.h"
 #include "mirror/array-inl.h"