Use class def index from java.lang.Class.

Bug: 10244719
Depends on:
https://googleplex-android-review.git.corp.google.com/362363
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.

Change-Id: I20c73a3b17d86286428ab0fd21bc13f51f36c85c
diff --git a/compiler/dex/frontend.h b/compiler/dex/frontend.h
index bafa468..6c33d10 100644
--- a/compiler/dex/frontend.h
+++ b/compiler/dex/frontend.h
@@ -117,7 +117,7 @@
                                                  const art::DexFile::CodeItem* code_item,
                                                  uint32_t access_flags,
                                                  art::InvokeType invoke_type,
-                                                 uint32_t class_dex_idx,
+                                                 uint16_t class_def_idx,
                                                  uint32_t method_idx,
                                                  jobject class_loader,
                                                  const art::DexFile& dex_file);