Add DCHECKs to ArenaVector and ScopedArenaVector.

Implement dchecked_vector<> template that DCHECK()s element
access and insert()/emplace()/erase() positions. Change the
ArenaVector<> and ScopedArenaVector<> aliases to use the new
template instead of std::vector<>. Remove DCHECK()s that
have now become unnecessary from the Optimizing compiler.

Change-Id: Ib8506bd30d223f68f52bd4476c76d9991acacadc
diff --git a/compiler/optimizing/pretty_printer.h b/compiler/optimizing/pretty_printer.h
index 34850a5..429e6e3 100644
--- a/compiler/optimizing/pretty_printer.h
+++ b/compiler/optimizing/pretty_printer.h
@@ -131,7 +131,7 @@
     PrintString("  ");
     PrintInt(gota->GetId());
     PrintString(": Goto ");
-    PrintInt(current_block_->GetSuccessor(0)->GetBlockId());
+    PrintInt(current_block_->GetSuccessors()[0]->GetBlockId());
     PrintNewLine();
   }