Opt compiler: Add disassembly to the '.cfg' output.

This is automatically added to the '.cfg' output when using the usual
`--dump-cfg` option.

Change-Id: I864bfc3a8299c042e72e451cc7730ad8271e4deb
diff --git a/compiler/optimizing/code_generator_mips64.h b/compiler/optimizing/code_generator_mips64.h
index 534154f..ec36496 100644
--- a/compiler/optimizing/code_generator_mips64.h
+++ b/compiler/optimizing/code_generator_mips64.h
@@ -228,6 +228,7 @@
   HGraphVisitor* GetLocationBuilder() OVERRIDE { return &location_builder_; }
   HGraphVisitor* GetInstructionVisitor() OVERRIDE { return &instruction_visitor_; }
   Mips64Assembler* GetAssembler() OVERRIDE { return &assembler_; }
+  const Mips64Assembler& GetAssembler() const OVERRIDE { return assembler_; }
 
   void MarkGCCard(GpuRegister object, GpuRegister value);