Convert Linkage to use MachineSignature.

src/compiler/common-operator.h

Index: src/compiler/common-operator.h
diff --git a/src/compiler/common-operator.h b/src/compiler/common-operator.h
index 65528e1d0c756189e03584fd3f6725559533aa79..d82c4bdcb1f57f90e54c29a22e885264549376e6 100644
--- a/src/compiler/common-operator.h
+++ b/src/compiler/common-operator.h
@@ -33,11 +33,14 @@ class ControlOperator : public Operator1<int> {
 
 class CallOperator : public Operator1<CallDescriptor*> {
  public:
+  // TODO(titzer): Operator still uses int, whereas CallDescriptor uses size_t.
   CallOperator(CallDescriptor* descriptor, const char* mnemonic)
       : Operator1<CallDescriptor*>(
             IrOpcode::kCall, descriptor->properties(),
-            descriptor->InputCount() + descriptor->FrameStateCount(),
-            descriptor->ReturnCount(), mnemonic, descriptor) {}
+            static_cast<int>(descriptor->InputCount() +
+                             descriptor->FrameStateCount()),
+            static_cast<int>(descriptor->ReturnCount()), mnemonic, descriptor) {
+  }
 
   virtual OStream& PrintParameter(OStream& os) const {  // NOLINT
     return os << "[" << *parameter() << "]";