Beginning support for library prefixes in the dart API.

runtime/bin/builtin.cc

Index: runtime/bin/builtin.cc
diff --git a/runtime/bin/builtin.cc b/runtime/bin/builtin.cc
index b2c7e0a22ef8de5dedeb39f75e09be7c46d4a0d6..98c20569ae8c67cdc843de404e857ff6e49c4507 100644
--- a/runtime/bin/builtin.cc
+++ b/runtime/bin/builtin.cc
@@ -26,8 +26,9 @@ static void ImportBuiltinLibIntoLib(
     const char* liburl, Dart_Handle builtin_lib) {
   Dart_Handle url = Dart_NewString(liburl);
   Dart_Handle lib = Dart_LookupLibrary(url);
+  Dart_Handle prefix = Dart_NewString("");
   DART_CHECK_VALID(lib);
-  DART_CHECK_VALID(Dart_LibraryImportLibrary(lib, builtin_lib));
+  DART_CHECK_VALID(Dart_LibraryImportLibrary(lib, builtin_lib, prefix));
 }
 
 
@@ -75,6 +76,9 @@ Dart_Handle Builtin::LoadLibrary(BuiltinLibraryId id) {
 
 void Builtin::ImportLibrary(Dart_Handle library, BuiltinLibraryId id) {
   Dart_Handle imported_library = LoadLibrary(id);
+  Dart_Handle prefix = Dart_NewString("");
   // Import the library into current library.
-  DART_CHECK_VALID(Dart_LibraryImportLibrary(library, imported_library));
+  DART_CHECK_VALID(Dart_LibraryImportLibrary(library,
+                                             imported_library,
+                                             prefix));
 }