jni: Fast path for @FastNative annotated java methods

Adds a faster path for java methods annotated with
dalvik.annotation.optimization.FastNative .

Intended to replace usage of fast JNI (registering with "!(FOO)BAR" descriptors).

Performance Microbenchmark Results (Angler):
* Regular JNI cost in nanoseconds: 115
* Fast JNI cost in nanoseconds: 60
* @FastNative cost in nanoseconds: 36

Summary: Up to 67% faster (vs fast jni) JNI transition cost

Change-Id: Ic23823ae0f232270c068ec999fd89aa993894b0e
diff --git a/runtime/well_known_classes.h b/runtime/well_known_classes.h
index c9faf69..b8e05b8 100644
--- a/runtime/well_known_classes.h
+++ b/runtime/well_known_classes.h
@@ -41,6 +41,7 @@
       SHARED_REQUIRES(Locks::mutator_lock_);
 
   static jclass com_android_dex_Dex;
+  static jclass dalvik_annotation_optimization_FastNative;
   static jclass dalvik_system_DexFile;
   static jclass dalvik_system_DexPathList;
   static jclass dalvik_system_DexPathList__Element;