jni: Add @CriticalNative optimization to speed up JNI transitions

Change-Id: I963059ac3a72dd8e6a867596c356d7062deb6da7
diff --git a/compiler/compiler.h b/compiler/compiler.h
index 9e5fb83..ed42958 100644
--- a/compiler/compiler.h
+++ b/compiler/compiler.h
@@ -39,8 +39,9 @@
   };
 
   enum JniOptimizationFlags {
-    kNone,
-    kFastNative,
+    kNone                       = 0x0,
+    kFastNative                 = 0x1,
+    kCriticalNative             = 0x2,
   };
 
   static Compiler* Create(CompilerDriver* driver, Kind kind);