ART: More header cleanup - runtime.h

Remove unnecessary runtime.h includes. Refactor other headers
(move to forward declarations) to make this possible.

Test: mmma art
Change-Id: I297f0ad444ba92169edd16d8c7cbe95bb6dbb800
diff --git a/runtime/class_linker.h b/runtime/class_linker.h
index 7f652ec..3d4bbc3 100644
--- a/runtime/class_linker.h
+++ b/runtime/class_linker.h
@@ -64,6 +64,7 @@
 template<typename T> class LengthPrefixedArray;
 template<class T> class MutableHandle;
 class InternTable;
+class LinearAlloc;
 class OatFile;
 template<class T> class ObjectLock;
 class Runtime;