[AST] Eliminate a few more LazyResolver::resolveDeclSignature() calls.

Author: DougGregor

lib/AST/Decl.cpp

@@ -3495,19 +3495,7 @@ bool ProtocolDecl::existentialTypeSupportedSlow(LazyResolver *resolver) {
   if (isObjC())
     return true;
 
-  // Resolve the protocol's type.
-  if (resolver && !hasInterfaceType())
-    resolver->resolveDeclSignature(this);
-
   for (auto member : getMembers()) {
-    if (auto vd = dyn_cast<ValueDecl>(member)) {
-      if (resolver && !vd->hasInterfaceType())
-        resolver->resolveDeclSignature(vd);
-    }
-
-    if (member->isInvalid())
-      continue;
-
     // Check for associated types.
     if (isa<AssociatedTypeDecl>(member)) {
       // An existential type cannot be used if the protocol has an
@@ -3524,6 +3512,9 @@ bool ProtocolDecl::existentialTypeSupportedSlow(LazyResolver *resolver) {
           continue;
       }
 
+      if (resolver && !valueMember->hasInterfaceType())
+        resolver->resolveDeclSignature(valueMember);
+
       if (!isAvailableInExistential(valueMember)) {
         Bits.ProtocolDecl.ExistentialTypeSupported = false;
         return false;