Emit declarations for typedefs that are needed by reflection.

sdk/lib/_internal/compiler/implementation/runtime_data.dart

Index: sdk/lib/_internal/compiler/implementation/runtime_data.dart
diff --git a/sdk/lib/_internal/compiler/implementation/runtime_data.dart b/sdk/lib/_internal/compiler/implementation/runtime_data.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0a5688dce52cf433fa2deeb39faf771a198069f6
--- /dev/null
+++ b/sdk/lib/_internal/compiler/implementation/runtime_data.dart
@@ -0,0 +1,18 @@
+/// Contains encoding, decoding and detection functionality for the
+/// representation of program data at runtime.
+///
+/// This library is shared between the compiler and the runtime system.
+library dart2js.runtime_data;
+
+
+String encodeTypedefFieldDescriptor(int typeIndex) {
+  return ":$typeIndex;";
+}
+
+bool isTypedefDescriptor(String descriptor) {
+  return descriptor.startsWith(':');
+}
+
+int getTypeFromTypedef(String descriptor) {
+  return int.parse(descriptor.substring(1, descriptor.length - 1));
+}