GC plugin: improve error reporting when tracing illegal fields.

tools/clang/blink_gc_plugin/Config.h

Index: tools/clang/blink_gc_plugin/Config.h
diff --git a/tools/clang/blink_gc_plugin/Config.h b/tools/clang/blink_gc_plugin/Config.h
index 53e52214de15e49915a854ca95c85bb8e4c984a6..8f494bbf2184a4cdefd9400d3d4ab1026870e626 100644
--- a/tools/clang/blink_gc_plugin/Config.h
+++ b/tools/clang/blink_gc_plugin/Config.h
@@ -49,12 +49,13 @@ class Config {
   }
 
   static bool IsPersistent(const std::string& name) {
-    return name == "Persistent";
+    return name == "Persistent" ||
+           name == "WeakPersistent" ;
   }
 
-  static bool IsPersistentHandle(const std::string& name) {
-    return IsPersistent(name) ||
-           IsPersistentGCCollection(name);
+  static bool IsCrossThreadPersistent(const std::string& name) {
+    return name == "CrossThreadPersistent" ||
+           name == "CrossThreadWeakPersistent" ;
   }
 
   static bool IsRefPtr(const std::string& name) {
@@ -65,6 +66,10 @@ class Config {
     return name == "OwnPtr";
   }
 
+  static bool IsUniquePtr(const std::string& name) {
+    return name == "unique_ptr";
+  }
+
   static bool IsWTFCollection(const std::string& name) {
     return name == "Vector" ||
            name == "Deque" ||