Add access to the isolate package-root/package-map in Platform.

runtime/bin/platform.cc

Index: runtime/bin/platform.cc
diff --git a/runtime/bin/platform.cc b/runtime/bin/platform.cc
index 0ed2bd364fd10eec6d347472f6233379e94a3cc1..dc12bc363001521c6a56a35040d19eca534efa84 100644
--- a/runtime/bin/platform.cc
+++ b/runtime/bin/platform.cc
@@ -76,15 +76,6 @@ void FUNCTION_NAME(Platform_ExecutableArguments)(Dart_NativeArguments args) {
 }
 
 
-void FUNCTION_NAME(Platform_PackageRoot)(Dart_NativeArguments args) {
-  const char* package_root = Platform::GetPackageRoot();
-  if (package_root == NULL) {
-    package_root = "";
-  }
-  Dart_SetReturnValue(args, Dart_NewStringFromCString(package_root));
-}
-
-
 void FUNCTION_NAME(Platform_Environment)(Dart_NativeArguments args) {
   intptr_t count = 0;
   char** env = Platform::Environment(&count);