ART: Some runtime cleanup

Use an enum for the compiler-callback mode.

Refactor and remove some unnecessary includes in runtime.h.

Change-Id: If2245fa470171311b8e05b677cf6bb28f209585a
diff --git a/runtime/noop_compiler_callbacks.h b/runtime/noop_compiler_callbacks.h
index a40659e..1cbf2bb 100644
--- a/runtime/noop_compiler_callbacks.h
+++ b/runtime/noop_compiler_callbacks.h
@@ -23,7 +23,7 @@
 
 class NoopCompilerCallbacks FINAL : public CompilerCallbacks {
  public:
-  NoopCompilerCallbacks() : CompilerCallbacks(false) {}
+  NoopCompilerCallbacks() : CompilerCallbacks(CompilerCallbacks::CallbackMode::kCompileApp) {}
   ~NoopCompilerCallbacks() {}
 
   bool MethodVerified(verifier::MethodVerifier* verifier ATTRIBUTE_UNUSED) OVERRIDE {