Use intersection of types as type of conditional

compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java

Index: compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
diff --git a/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java b/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
new file mode 100644
index 0000000000000000000000000000000000000000..4fcf9a24a5390088c11bf7c51b970cdc2b3d9ac3
--- /dev/null
+++ b/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
@@ -0,0 +1,98 @@
+// 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.
+
+package com.google.dart.compiler.type;
+
+import com.google.common.collect.ImmutableList;
+import com.google.dart.compiler.resolver.ClassElement;
+import com.google.dart.compiler.resolver.ClassElementUnion;
+
+import java.util.List;
+
+/**
+ * Artificial {@link InterfaceType} which is union of several {@link InterfaceType}s.
+ */
+class InterfaceTypeUnion implements InterfaceType {
+  
+  private final List<InterfaceType> types;
+  private final ClassElement element;
+
+  public InterfaceTypeUnion(List<InterfaceType> types) {
+    this.types = types;
+    this.element = new ClassElementUnion(this, types);
+  }
+  
+  @Override
+  public boolean equals(Object obj) {
+    if (obj instanceof InterfaceTypeUnion) {
+      InterfaceTypeUnion other = (InterfaceTypeUnion) obj;
+      return getElement().equals(other.getElement());
+    }
+    return false;
+  }
+
+  @Override
+  public int hashCode() {
+    int hashCode = 31;
+    hashCode += getElement().hashCode();
+    hashCode += 31 * hashCode + getArguments().hashCode();
+    return hashCode;
+  }
+
+  @Override
+  public String toString() {
+    return types.toString();
+  }
+  
+  @Override
+  public TypeKind getKind() {
+    return TypeKind.INTERFACE;
+  }
+
+  @Override
+  public boolean isInferred() {
+    return false;
+  }
+
+  @Override
+  public InterfaceType subst(List<Type> arguments, List<Type> parameters) {
+    return null;
+  }
+
+  @Override
+  public ClassElement getElement() {
+    return element;
+  }
+
+  @Override
+  public List<Type> getArguments() {
+    return ImmutableList.of();
+  }
+
+  @Override
+  public boolean isRaw() {
+    return true;
+  }
+
+  @Override
+  public boolean hasDynamicTypeArgs() {
+    return false;
+  }
+
+  @Override
+  public InterfaceType asRawType() {
+    return this;
+  }
+
+  @Override
+  public Member lookupMember(String name) {
+    for (InterfaceType type : types) {
+      Member member = type.lookupMember(name);
+      if (member != null) {
+        return member;
+      }
+    }
+    return null;
+  }
+}