Replace TypeMask.isEmpty by isEmptyOrNull, use isEmpty when it's really empty.

pkg/compiler/lib/src/cps_ir/inline.dart

Index: pkg/compiler/lib/src/cps_ir/inline.dart
diff --git a/pkg/compiler/lib/src/cps_ir/inline.dart b/pkg/compiler/lib/src/cps_ir/inline.dart
index 6c9f30ca720dc91cf18de0444a25d503c46a8617..b341869dba88569b615ccb131d6c0427b426ff6f 100644
--- a/pkg/compiler/lib/src/cps_ir/inline.dart
+++ b/pkg/compiler/lib/src/cps_ir/inline.dart
@@ -431,7 +431,7 @@ class InliningVisitor extends TrampolineRecursiveVisitor {
 
     // Don't inline methods that never return. They are usually helper functions
     // that throw an exception.
-    if (invoke.type.isEmpty && !invoke.type.isNullable) {
+    if (invoke.type.isEmpty) {
       // TODO(sra): It would be ok to inline if doing so was shrinking.
       return null;
     }
@@ -451,7 +451,7 @@ class InliningVisitor extends TrampolineRecursiveVisitor {
     // to be `null` (isEmpty covers `null` and unreachable).
     TypeMask abstractReceiverInMethod = abstractReceiver == null
         ? null
-        : abstractReceiver.isEmpty
+        : abstractReceiver.isEmptyOrNull
             ? abstractReceiver
             : abstractReceiver.nonNullable();
     List<TypeMask> abstractArguments =