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.cc b/runtime/well_known_classes.cc
index 48deb35..ddce344 100644
--- a/runtime/well_known_classes.cc
+++ b/runtime/well_known_classes.cc
@@ -30,6 +30,7 @@
 namespace art {
 
 jclass WellKnownClasses::com_android_dex_Dex;
+jclass WellKnownClasses::dalvik_annotation_optimization_FastNative;
 jclass WellKnownClasses::dalvik_system_DexFile;
 jclass WellKnownClasses::dalvik_system_DexPathList;
 jclass WellKnownClasses::dalvik_system_DexPathList__Element;
@@ -215,6 +216,7 @@
 
 void WellKnownClasses::Init(JNIEnv* env) {
   com_android_dex_Dex = CacheClass(env, "com/android/dex/Dex");
+  dalvik_annotation_optimization_FastNative = CacheClass(env, "dalvik/annotation/optimization/FastNative");
   dalvik_system_DexFile = CacheClass(env, "dalvik/system/DexFile");
   dalvik_system_DexPathList = CacheClass(env, "dalvik/system/DexPathList");
   dalvik_system_DexPathList__Element = CacheClass(env, "dalvik/system/DexPathList$Element");