Introduce initial plumbing for type promotion in fasta.

pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart
index d8fb64f4db7481409c1cedcc03a6c3e19bc1974e..2d0651be0b50f28d241d9b5d6cf7943403d0f951 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart
@@ -2,29 +2,56 @@
 // 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.
 
+import 'package:front_end/src/fasta/type_inference/type_promotion.dart';
 import 'package:kernel/ast.dart';
 
 import '../builder/ast_factory.dart';
 import 'kernel_shadow_ast.dart';
 
 /// Concrete implementation of [builder.AstFactory] for building a kernel AST.
-class KernelAstFactory implements AstFactory {
+class KernelAstFactory implements AstFactory<VariableDeclaration> {
   @override
   KernelBlock block(List<Statement> statements, int charOffset) {
     return new KernelBlock(statements)..fileOffset = charOffset;
   }
 
   @override
+  ExpressionStatement expressionStatement(Expression expression) {
+    return new KernelExpressionStatement(expression);
+  }
+
+  @override
   Field field(Name name, int charOffset, {String fileUri}) {
     return new KernelField(name, fileUri: fileUri)..fileOffset = charOffset;
   }
 
   @override
+  FunctionExpression functionExpression(FunctionNode function, int charOffset) {
+    return new KernelFunctionExpression(function)..fileOffset = charOffset;
+  }
+
+  @override
+  Statement ifStatement(
+      Expression condition, Statement thenPart, Statement elsePart) {
+    return new KernelIfStatement(condition, thenPart, elsePart);
+  }
+
+  @override
   KernelIntLiteral intLiteral(value, int charOffset) {
     return new KernelIntLiteral(value)..fileOffset = charOffset;
   }
 
   @override
+  Expression isExpression(
+      Expression expression, DartType type, int charOffset, bool isInverted) {
+    if (isInverted) {
+      return new KernelIsNotExpression(expression, type, charOffset);
+    } else {
+      return new KernelIsExpression(expression, type)..fileOffset = charOffset;
+    }
+  }
+
+  @override
   KernelListLiteral listLiteral(List<Expression> expressions,
       DartType typeArgument, bool isConst, int charOffset) {
     return new KernelListLiteral(expressions,
@@ -48,13 +75,14 @@ class KernelAstFactory implements AstFactory {
   }
 
   @override
-  KernelVariableDeclaration variableDeclaration(String name, int charOffset,
+  VariableDeclaration variableDeclaration(
+      String name, int charOffset, int functionNestingLevel,
       {DartType type,
       Expression initializer,
       int equalsCharOffset = TreeNode.noOffset,
       bool isFinal: false,
       bool isConst: false}) {
-    return new KernelVariableDeclaration(name,
+    return new KernelVariableDeclaration(name, functionNestingLevel,
         type: type,
         initializer: initializer,
         isFinal: isFinal,
@@ -62,4 +90,14 @@ class KernelAstFactory implements AstFactory {
       ..fileOffset = charOffset
       ..fileEqualsOffset = equalsCharOffset;
   }
+
+  @override
+  VariableGet variableGet(
+      VariableDeclaration variable,
+      TypePromotionFact<VariableDeclaration> fact,
+      TypePromotionScope scope,
+      int charOffset) {
+    return new KernelVariableGet(variable, fact, scope)
+      ..fileOffset = charOffset;
+  }
 }