Make isEmpty a getter.

lib/compiler/implementation/ssa/types_propagation.dart

Index: lib/compiler/implementation/ssa/types_propagation.dart
diff --git a/lib/compiler/implementation/ssa/types_propagation.dart b/lib/compiler/implementation/ssa/types_propagation.dart
index 377f233b0f402ebabd7926aecf9a3e5ae0250e7c..54b69de6f46a96dca73440827d77972b4094a472 100644
--- a/lib/compiler/implementation/ssa/types_propagation.dart
+++ b/lib/compiler/implementation/ssa/types_propagation.dart
@@ -98,7 +98,7 @@ class SsaTypePropagator extends HGraphVisitor implements OptimizationPhase {
 
   void processWorklist() {
     do {
-      while (!worklist.isEmpty()) {
+      while (!worklist.isEmpty) {
         int id = worklist.removeLast();
         HInstruction instruction = workmap[id];
         assert(instruction != null);
@@ -112,7 +112,7 @@ class SsaTypePropagator extends HGraphVisitor implements OptimizationPhase {
       // replaced operands, so we may need to take another stab at
       // emptying the worklist afterwards.
       processPendingOptimizations();
-    } while (!worklist.isEmpty());
+    } while (!worklist.isEmpty);
   }
 
   void addDependentInstructionsToWorkList(HInstruction instruction) {