More -fsanitize=vptr fixes.

src/compiler/instruction-selector-impl.h

Index: src/compiler/instruction-selector-impl.h
diff --git a/src/compiler/instruction-selector-impl.h b/src/compiler/instruction-selector-impl.h
index d1e27f0466d1c71b40913f06ec1ddcec6c304e3a..bdcd952b5f703a60aa18a4813325dd2b24ae0f91 100644
--- a/src/compiler/instruction-selector-impl.h
+++ b/src/compiler/instruction-selector-impl.h
@@ -338,10 +338,10 @@ class FlagsContinuation FINAL {
 // TODO(bmeurer): Get rid of the CallBuffer business and make
 // InstructionSelector::VisitCall platform independent instead.
 struct CallBuffer {
-  CallBuffer(Zone* zone, CallDescriptor* descriptor,
+  CallBuffer(Zone* zone, const CallDescriptor* descriptor,
              FrameStateDescriptor* frame_state);
 
-  CallDescriptor* descriptor;
+  const CallDescriptor* descriptor;
   FrameStateDescriptor* frame_state_descriptor;
   NodeVector output_nodes;
   InstructionOperandVector outputs;