Revert "Collect the types used in is-checks in the resolver phase."

lib/compiler/implementation/typechecker.dart

Index: lib/compiler/implementation/typechecker.dart
diff --git a/lib/compiler/implementation/typechecker.dart b/lib/compiler/implementation/typechecker.dart
index 8f75031f31160a0f8bcaf7d2538dd6b03b59ebf4..fc82c88311e9514d7b9eadbbafb61a800efa1a99 100644
--- a/lib/compiler/implementation/typechecker.dart
+++ b/lib/compiler/implementation/typechecker.dart
@@ -24,9 +24,9 @@ class TypeCheckerTask extends CompilerTask {
   }
 }
 
-abstract class DartType implements Hashable {
-  abstract SourceString get name();
-  abstract Element get element();
+interface DartType {
+  SourceString get name();
+  Element get element();
 
   /**
    * Returns the unaliased type of this type.
@@ -38,9 +38,7 @@ abstract class DartType implements Hashable {
    * function type [: (B) -> A :] and the unaliased type of
    * [: Func<int,String> :] is the function type [: (String) -> int :].
    */
-  abstract DartType unalias(Compiler compiler);
-
-  abstract bool equals(other);
+  DartType unalias(Compiler compiler);
 }
 
 class TypeVariableType implements DartType {
@@ -52,13 +50,6 @@ class TypeVariableType implements DartType {
 
   DartType unalias(Compiler compiler) => this;
 
-  int hashCode() => 17 * element.hashCode();
-
-  bool equals(other) {
-    if (other is !TypeVariableType) return false;
-    return other.element == element;
-  }
-
   String toString() => name.slowToString();
 }
 
@@ -84,13 +75,6 @@ class StatementType implements DartType {
 
   DartType unalias(Compiler compiler) => this;
 
-  int hashCode() => 17 * stringName.hashCode();
-
-  bool equals(other) {
-    if (other is !StatementType) return false;
-    return other.stringName == stringName;
-  }
-
   String toString() => stringName;
 }
 
@@ -101,10 +85,6 @@ class VoidType implements DartType {
 
   DartType unalias(Compiler compiler) => this;
 
-  int hashCode() => 1729;
-
-  bool equals(other) => other is VoidType;
-
   String toString() => name.slowToString();
 }
 
@@ -129,22 +109,6 @@ class InterfaceType implements DartType {
     }
     return sb.toString();
   }
-
-  int hashCode() {
-    int hash = element.hashCode();
-    for (Link<DartType> arguments = this.arguments;
-         !arguments.isEmpty();
-         arguments = arguments.tail) {
-      int argumentHash = arguments.head != null ? arguments.head.hashCode() : 0;
-      hash = 17 * hash + 3 * argumentHash;
-    }
-    return hash;
-  }
-
-  bool equals(other) {
-    if (other is !InterfaceType) return false;
-    return arguments == other.arguments;
-  }
 }
 
 class FunctionType implements DartType {
@@ -180,22 +144,6 @@ class FunctionType implements DartType {
     returnType = other.returnType;
     parameterTypes = other.parameterTypes;
   }
-
-  int hashCode() {
-    int hash = 17 * element.hashCode() + 3 * returnType.hashCode();
-    for (Link<DartType> parameters = parameterTypes;
-         !parameters.isEmpty();
-        parameters = parameters.tail) {
-      hash = 17 * hash + 3 * parameters.head.hashCode();
-    }
-    return hash;
-  }
-
-  bool equals(other) {
-    if (other is !FunctionType) return false;
-    return returnType == other.returnType
-           && parameterTypes == other.parameterTypes;
-  }
 }
 
 class TypedefType implements DartType {
@@ -223,13 +171,6 @@ class TypedefType implements DartType {
     }
     return sb.toString();
   }
-
-  int hashCode() => 17 * element.hashCode();
-
-  bool equals(other) {
-    if (other is !TypedefType) return false;
-    return other.element == element;
-  }
 }
 
 class Types {