Use class def index from java.lang.Class.

Bug: 10244719
This removes the computation of the dex file index, when necessary this is
computed by searching the dex file. Its only necessary in
dalvik.system.DexFile.defineClassNative and DexFile::FindInClassPath, the
latter not showing up significantly in profiling with this change.

(cherry-picked from 8b2c0b9abc3f520495f4387ea040132ba85cae69)
Change-Id: I20c73a3b17d86286428ab0fd21bc13f51f36c85c
diff --git a/runtime/Android.mk b/runtime/Android.mk
index a8d505e..a0ae4bf 100644
--- a/runtime/Android.mk
+++ b/runtime/Android.mk
@@ -92,6 +92,7 @@
 	native/dalvik_system_VMStack.cc \
 	native/dalvik_system_Zygote.cc \
 	native/java_lang_Class.cc \
+	native/java_lang_DexCache.cc \
 	native/java_lang_Object.cc \
 	native/java_lang_Runtime.cc \
 	native/java_lang_String.cc \