Update incremental load example so you can point to different sdk

pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart

Index: pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart
diff --git a/pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart b/pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart
index b725d76460c9696adf60f097f4db654180a1c3e1..64d01468335af6c3de6fd0c8c38cc8aca392f7bc 100644
--- a/pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart
+++ b/pkg/front_end/example/incremental_reload/compiler_with_invalidation.dart
@@ -23,10 +23,10 @@ import 'package:kernel/binary/limited_ast_to_binary.dart';
 /// results.
 // TODO(sigmund): make this example work outside of the SDK repo.
 Future<IncrementalCompiler> createIncrementalCompiler(String entry,
-    {bool persistent: true}) {
+    {bool persistent: true, Uri argSdkRoot}) {

[Siggi Cherem (dart-lang), 2017/08/15 00:37:14]

nit: rename to sdkRoot, possibly remove the TODO :) above?

[aam, 2017/08/15 03:59:49]

Done.

   var entryUri = Uri.base.resolve(entry);
   var dartVm = Uri.base.resolve(Platform.resolvedExecutable);
-  var sdkRoot = dartVm.resolve("patched_sdk/");
+  var sdkRoot = argSdkRoot ?? dartVm.resolve("patched_sdk/");
   var tmpDir = Directory.systemTemp.createTempSync('ikg_cache');
   var options = new CompilerOptions()
     ..sdkRoot = sdkRoot