Treat ambiguous types as malformed.

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 1099 matching lines @@
   }
 
   HInstruction convertType(Compiler compiler, DartType type, int kind) {
     if (type == null) return this;
     type = type.unalias(compiler);
     // Only the builder knows how to create [HTypeConversion]
     // instructions with generics. It has the generic type context
     // available.
     assert(type.kind != TypeKind.TYPE_VARIABLE);
     assert(type.isRaw || type.kind == TypeKind.FUNCTION);
-    if (type.containsAmbiguousTypes) {
-      return new HTypeConversion(type, kind, HType.UNKNOWN, this);
-    }
     if (type.treatAsDynamic) return this;
     if (identical(type.element, compiler.objectClass)) return this;
     if (type.kind != TypeKind.INTERFACE) {
       return new HTypeConversion(type, kind, HType.UNKNOWN, this);
     } else if (kind == HTypeConversion.BOOLEAN_CONVERSION_CHECK) {
       // Boolean conversion checks work on non-nullable booleans.
       return new HTypeConversion(type, kind, HType.BOOLEAN, this);
     } else if (kind == HTypeConversion.CHECKED_MODE_CHECK && !type.isRaw) {
         throw 'creating compound check to $type (this = ${this})';
     } else {
@@ skipping 1581 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }