Add trampoline symbols to native debug info.

The debugger needs them to unwind through the trampolines and to
understand what is happening in the call stack.

Change-Id: Ia554058c3796788adcd7336d620a7734eb366905
diff --git a/compiler/debug/elf_debug_line_writer.h b/compiler/debug/elf_debug_line_writer.h
index ed26d96..9875c71 100644
--- a/compiler/debug/elf_debug_line_writer.h
+++ b/compiler/debug/elf_debug_line_writer.h
@@ -117,6 +117,7 @@
       Elf_Addr method_address = base_address + mi->code_address;
 
       PositionInfos dex2line_map;
+      DCHECK(mi->dex_file != nullptr);
       const DexFile* dex = mi->dex_file;
       if (!dex->DecodeDebugPositionInfo(mi->code_item, PositionInfoCallback, &dex2line_map)) {
         continue;