First step towards having patch files for generic libraries.

lib/compiler/implementation/apiimpl.dart

Index: lib/compiler/implementation/apiimpl.dart
diff --git a/lib/compiler/implementation/apiimpl.dart b/lib/compiler/implementation/apiimpl.dart
index ff5c5dce481ce81451abb29874dd4fb4139a858b..8d6c88c36860ae6a0b300901888e829b91179b11 100644
--- a/lib/compiler/implementation/apiimpl.dart
+++ b/lib/compiler/implementation/apiimpl.dart
@@ -33,7 +33,7 @@ class Compiler extends leg.Compiler {
           validateUnparse: options.indexOf('--unparse-validation') !== -1);
 
   elements.LibraryElement scanBuiltinLibrary(String path) {
-    Uri uri = libraryRoot.resolve(DART2JS_LIBRARY_MAP[path]);
+    Uri uri = libraryRoot.resolve(DART2JS_LIBRARY_MAP[path].libraryPath);
     elements.LibraryElement library = scanner.loadLibrary(uri, null);
     return library;
   }
@@ -70,7 +70,7 @@ class Compiler extends leg.Compiler {
   }
 
   Uri translateDartUri(Uri uri, tree.Node node) {
-    String path = DART2JS_LIBRARY_MAP[uri.path];
+    String path = DART2JS_LIBRARY_MAP[uri.path].libraryPath;
     if (path === null || uri.path.startsWith('_')) {
       reportError(node, 'library not found ${uri}');
       return null;
@@ -84,6 +84,12 @@ class Compiler extends leg.Compiler {
     return libraryRoot.resolve(path);
   }
 
+  Uri resolvePatchUri(String dartLibraryPath) {
+    String patchPath = DART2JS_LIBRARY_MAP[dartLibraryPath].patchPath;
+    if (patchPath === null) return null;
+    return libraryRoot.resolve(patchPath);
+  }
+
   translatePackageUri(Uri uri, tree.Node node) => packageRoot.resolve(uri.path);
 
   bool run(Uri uri) {