Make reflectClassByName work with interceptor names.

sdk/lib/_internal/lib/js_mirrors.dart

Index: sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/lib/js_mirrors.dart b/sdk/lib/_internal/lib/js_mirrors.dart
index 5d077a4bfb7d70e8264a95443da48fbe21aef006..4c6df6230f940021ba79dcb12f6f60cb64bf7e65 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -524,6 +524,12 @@ TypeMirror reflectClassByMangledName(String mangledName) {
 var classMirrors;
 
 TypeMirror reflectClassByName(Symbol symbol, String mangledName) {
+  int separatorIndex = mangledName.indexOf('/');
+  if (separatorIndex > -1) {
+    // This is an interceptor name, where the first part is the nice name used
+    // for printing the type name.
+    mangledName = mangledName.substring(separatorIndex + 1);
+  }
   if (classMirrors == null) classMirrors = JsCache.allocate();
   var mirror = JsCache.fetch(classMirrors, mangledName);
   if (mirror != null) return mirror;