Add import/export declaration AST node boilerplate to kernel.

pkg/compiler/lib/src/kernel/kernel_visitor.dart

Index: pkg/compiler/lib/src/kernel/kernel_visitor.dart
diff --git a/pkg/compiler/lib/src/kernel/kernel_visitor.dart b/pkg/compiler/lib/src/kernel/kernel_visitor.dart
index a5523f81ec7d04392998cd9748067e4b45e2d6a8..69fae3817eb167c8e5f225969367cfbfe1e37d20 100644
--- a/pkg/compiler/lib/src/kernel/kernel_visitor.dart
+++ b/pkg/compiler/lib/src/kernel/kernel_visitor.dart
@@ -209,8 +209,8 @@ class KernelVisitor extends Object
   // object, via the prefix name (aka "bar" in
   // "import foo.dart deferred as bar"). LibraryElement corresponds to the
   // imported library element.
-  final Map<LibraryElement, Map<String, ir.DeferredImport>> deferredImports =
-      <LibraryElement, Map<String, ir.DeferredImport>>{};
+  final Map<LibraryElement, Map<String, ir.LibraryDependency>> deferredImports =
+      <LibraryElement, Map<String, ir.LibraryDependency>>{};
 
   ir.Node associateElement(ir.Node node, Element element) {
     kernel.nodeToElement[node] = element;
@@ -226,7 +226,7 @@ class KernelVisitor extends Object
 
   /// If non-null, reference to a deferred library that a subsequent getter is
   /// using.
-  ir.DeferredImport _deferredLibrary;
+  ir.LibraryDependency _deferredLibrary;
 
   KernelVisitor(this.currentElement, this.elements, this.kernel);
 
@@ -2286,11 +2286,11 @@ class KernelVisitor extends Object
     return buildIrFunction(ir.ProcedureKind.Getter, getter, body);
   }
 
-  ir.DeferredImport getDeferredImport(PrefixElement prefix) {
+  ir.LibraryDependency getDeferredImport(PrefixElement prefix) {
     var map = deferredImports[prefix.deferredImport.importedLibrary] ??=
-        <String, ir.DeferredImport>{};
+        <String, ir.LibraryDependency>{};
     return map[prefix.name] ??= associateElement(
-        new ir.DeferredImport(
+        new ir.LibraryDependency.deferredImport(
             kernel.libraries[prefix.deferredImport.importedLibrary],
             prefix.name),
         prefix);
@@ -2755,7 +2755,7 @@ class KernelVisitor extends Object
   /// deferredImport is null, then the function returned is the identity
   /// expression. Otherwise, it inserts a CheckLibraryIsLoaded call before
   /// evaluating the expression.
-  _createCheckLibraryLoadedFuncIfNeeded(ir.DeferredImport deferredImport) {
+  _createCheckLibraryLoadedFuncIfNeeded(ir.LibraryDependency deferredImport) {
     if (deferredImport != null) {
       return (ir.Expression inputExpression) => new ir.Let(
           makeOrReuseVariable(new ir.CheckLibraryIsLoaded(deferredImport)),