dart2js: add support for configuration-specific imports.

pkg/compiler/lib/src/tree/prettyprint.dart

Index: pkg/compiler/lib/src/tree/prettyprint.dart
diff --git a/pkg/compiler/lib/src/tree/prettyprint.dart b/pkg/compiler/lib/src/tree/prettyprint.dart
index 5096e7407b09d7c378c39195f79de05a5b4048bd..552747e1e2cb73dd2dbf1a849a3d797694da2c31 100644
--- a/pkg/compiler/lib/src/tree/prettyprint.dart
+++ b/pkg/compiler/lib/src/tree/prettyprint.dart
@@ -88,10 +88,20 @@ class PrettyPrinter extends Indentation with Tagging<Node> implements Visitor {
     visitNodeWithChildren(node, "Conditional");
   }
 
+  visitConditionalUri(ConditionalUri node) {
+    visitNodeWithChildren(node, "ConditionalUri");
+  }
+
   visitContinueStatement(ContinueStatement node) {
     visitNodeWithChildren(node, "ContinueStatement");
   }
 
+  visitDottedName(DottedName node) {
+    openNode(node, "DottedName");
+    visitChildNode(node.identifiers, "identifiers");
+    closeNode();
+  }
+
   visitDoWhile(DoWhile node) {
     visitNodeWithChildren(node, "DoWhile");
   }
@@ -380,6 +390,9 @@ class PrettyPrinter extends Indentation with Tagging<Node> implements Visitor {
   visitExport(Export node) {
     openNode(node, "Export");
     visitChildNode(node.uri, "uri");
+    if (node.conditionalUris != null) {
+      visitChildNode(node.conditionalUris, "conditionalUris");
+    }
     visitChildNode(node.combinators, "combinators");
     closeNode();
   }
@@ -388,6 +401,9 @@ class PrettyPrinter extends Indentation with Tagging<Node> implements Visitor {
     openNode(node, "Import", {
       "isDeferred" : "${node.isDeferred}"});
     visitChildNode(node.uri, "uri");
+    if (node.conditionalUris != null) {
+      visitChildNode(node.conditionalUris, "conditionalUris");
+    }
     visitChildNode(node.combinators, "combinators");
     if (node.prefix != null) {
       visitChildNode(node.prefix, "prefix");