Break apart header files.

Create libart-gtest for common runtime and compiler gtest routines.
Rename CompilerCallbacksImpl that is quick compiler specific.
Rename trace clock source constants to not use the overloaded profiler term.

Change-Id: I4aac4bdc7e7850c68335f81e59a390133b54e933
diff --git a/runtime/mirror/string.h b/runtime/mirror/string.h
index 8ab4db9..46bdd59 100644
--- a/runtime/mirror/string.h
+++ b/runtime/mirror/string.h
@@ -19,6 +19,7 @@
 
 #include <gtest/gtest.h>
 
+#include "object.h"
 #include "object_callbacks.h"
 #include "read_barrier.h"