Revert "dart2js cps_ir: Seed type_propagation with constant bools from inference."

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

Index: pkg/compiler/lib/src/cps_ir/type_mask_system.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
index 8aa987c192e97376a7a39d7ddb445634171e6ab9..c911b5f6279930e47aa841f36c6fb7180ba4c889 100644
--- a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
@@ -127,19 +127,6 @@ class TypeMaskSystem {
     return computeTypeMask(inferrer.compiler, constant);
   }
 
-  // Returns the constant value if a TypeMask represents a single value.
-  // Returns `null` if [mask] is not a constant.
-  ConstantValue getConstantOf(TypeMask mask) {
-    if (!mask.isValue) return null;
-    ValueTypeMask valueMask = mask;
-    var value = valueMask.value;
-    // TODO(sra): Why is ValueTypeMask.value not a ConstantValue?
-    if (value == false) return new FalseConstantValue();
-    if (value == true) return new TrueConstantValue();
-    // TODO(sra): Consider other values. Be careful with large strings.
-    return null;
-  }
-
   TypeMask nonNullExact(ClassElement element) {
     // The class world does not know about classes created by
     // closure conversion, so just treat those as a subtypes of Function.