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/compiler/driver/dex_compilation_unit.cc b/compiler/driver/dex_compilation_unit.cc
index eb8941b..c441d09 100644
--- a/compiler/driver/dex_compilation_unit.cc
+++ b/compiler/driver/dex_compilation_unit.cc
@@ -39,7 +39,7 @@
                                        ClassLinker* class_linker,
                                        const DexFile& dex_file,
                                        const DexFile::CodeItem* code_item,
-                                       uint32_t class_def_idx,
+                                       uint16_t class_def_idx,
                                        uint32_t method_idx,
                                        uint32_t access_flags)
     : cu_(cu),