dart2js: add support for configuration-specific imports.

pkg/compiler/lib/src/parser/element_listener.dart

Index: pkg/compiler/lib/src/parser/element_listener.dart
diff --git a/pkg/compiler/lib/src/parser/element_listener.dart b/pkg/compiler/lib/src/parser/element_listener.dart
index 0cdf72ed1dd720c6c44d70f65d949e73449ad4de..fb5314ef8dc8181f0f8a68b595749b786e09b431 100644
--- a/pkg/compiler/lib/src/parser/element_listener.dart
+++ b/pkg/compiler/lib/src/parser/element_listener.dart
@@ -150,12 +150,34 @@ class ElementListener extends Listener {
     if (asKeyword != null) {
       prefix = popNode();
     }
+    NodeList conditionalUris = popNode();
     StringNode uri = popLiteralString();
-    addLibraryTag(new Import(importKeyword, uri, prefix, combinators,
+    addLibraryTag(new Import(importKeyword, uri, conditionalUris,
+                             prefix, combinators,
                              popMetadata(compilationUnitElement),
                              isDeferred: isDeferred));
   }
 
+  void endDottedName(int count, Token token) {
+    NodeList identifiers = makeNodeList(count, null, null, '.');
+    pushNode(new DottedName(token, identifiers));
+  }
+
+  void endConditionalUris(int count) {
+    if (count == 0) {
+      pushNode(null);
+    } else {
+      pushNode(makeNodeList(count, null, null, " "));
+    }
+  }
+
+  void endConditionalUri(Token ifToken, Token equalSign) {
+    StringNode uri = popNode();
+    LiteralString conditionValue = (equalSign != null) ? popNode() : null;
+    DottedName identifier = popNode();
+    pushNode(new ConditionalUri(ifToken, identifier, conditionValue, uri));
+  }
+
   void endEnum(Token enumKeyword, Token endBrace, int count) {
     NodeList names = makeNodeList(count, enumKeyword.next.next, endBrace, ",");
     Identifier name = popNode();
@@ -169,8 +191,9 @@ class ElementListener extends Listener {
 
   void endExport(Token exportKeyword, Token semicolon) {
     NodeList combinators = popNode();
+    NodeList conditionalUris = popNode();
     StringNode uri = popNode();
-    addLibraryTag(new Export(exportKeyword, uri, combinators,
+    addLibraryTag(new Export(exportKeyword, uri, conditionalUris, combinators,
                              popMetadata(compilationUnitElement)));
   }