Make sure that when a SupportsUserData is destroyed, objects destroyed transitively see it as empty.

base/supports_user_data.cc

Index: base/supports_user_data.cc
diff --git a/base/supports_user_data.cc b/base/supports_user_data.cc
index 2a0263ed0d1881e6552f04b44a34fadf3e441cb2..8c6bf9116a13fb54536367bcee489bf77d393600 100644
--- a/base/supports_user_data.cc
+++ b/base/supports_user_data.cc
@@ -35,6 +35,11 @@ void SupportsUserData::DetachUserDataThread() {
 
 SupportsUserData::~SupportsUserData() {
   DCHECK(thread_checker_.CalledOnValidThread() || user_data_.empty());
+  DataMap local_user_data;
+  user_data_.swap(local_user_data);
+  // Now this->user_data_ is empty, and any destructors called transitively from
+  // the destruction of |local_user_data| will see it that way instead of
+  // calling into a being-destroyed object.

[Peter Kasting, 2014/05/28 03:44:13]

Nit: calling into -> examining

[Jeffrey Yasskin, 2014/05/28 05:45:26]

Done.

 }
 
 }  // namespace base