dart2js: add support for configuration-specific imports.

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

Index: pkg/compiler/lib/src/parser/parser.dart
diff --git a/pkg/compiler/lib/src/parser/parser.dart b/pkg/compiler/lib/src/parser/parser.dart
index 6ed2657b74a53e158e607f8e2b38a95ab8db671c..c88f20df9519930d39fc782a8d9e41e17899fca2 100644
--- a/pkg/compiler/lib/src/parser/parser.dart
+++ b/pkg/compiler/lib/src/parser/parser.dart
@@ -99,11 +99,14 @@ class FormalParameterType {
 class Parser {
   final Listener listener;
   bool mayParseFunctionExpressions = true;
+  final bool enableConditionalDirectives;
   bool yieldIsKeyword;
   bool awaitIsKeyword;
 
   Parser(this.listener,
-         {this.yieldIsKeyword: false, this.awaitIsKeyword: false});
+      {this.enableConditionalDirectives: false,
+       this.yieldIsKeyword: false,
+       this.awaitIsKeyword: false});
 
   Token parseUnit(Token token) {
     listener.beginCompilationUnit(token);
@@ -152,12 +155,13 @@ class Parser {
     return token;
   }
 
-  /// import uri (as identifier)? combinator* ';'
+  /// import uri (if (test) uri)* (as identifier)? combinator* ';'
   Token parseImport(Token token) {
     Token importKeyword = token;
     listener.beginImport(importKeyword);
     assert(optional('import', token));
     token = parseLiteralStringOrRecoverExpression(token.next);
+    token = parseConditionalUris(token);
     Token deferredKeyword;
     if (optional('deferred', token)) {
       deferredKeyword = token;
@@ -175,12 +179,57 @@ class Parser {
     return token;
   }
 
-  /// export uri combinator* ';'
+  /// if (test) uri
+  Token parseConditionalUris(Token token) {
+    listener.beginConditionalUris(token);
+    int count = 0;
+    if (enableConditionalDirectives) {
+      while (optional('if', token)) {
+        count++;
+        token = parseConditionalUri(token);
+      }
+    }
+    listener.endConditionalUris(count);
+    return token;
+  }
+
+  Token parseConditionalUri(Token token) {
+    listener.beginConditionalUri(token);
+    Token ifKeyword = token;
+    token = expect('if', token);
+    token = expect('(', token);
+    token = parseDottedName(token);
+    Token equalitySign;
+    if (optional('==', token)) {
+      equalitySign = token;
+      token = parseLiteralStringOrRecoverExpression(token.next);
+    }
+    token = expect(')', token);
+    token = parseLiteralStringOrRecoverExpression(token);
+    listener.endConditionalUri(ifKeyword, equalitySign);
+    return token;
+  }
+
+  Token parseDottedName(Token token) {
+    listener.beginDottedName(token);
+    Token firstIdentifier = token;
+    token = parseIdentifier(token);
+    int count = 1;
+    while (optional('.', token)) {
+      token = parseIdentifier(token.next);
+      count++;
+    }
+    listener.endDottedName(count, firstIdentifier);
+    return token;
+  }
+
+  /// export uri conditional-uris* combinator* ';'
   Token parseExport(Token token) {
     Token exportKeyword = token;
     listener.beginExport(exportKeyword);
     assert(optional('export', token));
     token = parseLiteralStringOrRecoverExpression(token.next);
+    token = parseConditionalUris(token);
     token = parseCombinators(token);
     Token semicolon = token;
     token = expect(';', token);