[Extensions] Fix thread-safety bug in PermissionsData

extensions/common/permissions/permissions_data.h

Index: extensions/common/permissions/permissions_data.h
diff --git a/extensions/common/permissions/permissions_data.h b/extensions/common/permissions/permissions_data.h
index e0f9b107a3b567e15da6797fc053410263206275..d3238b11fd81b269e583798fb0e3542a62dd0933 100644
--- a/extensions/common/permissions/permissions_data.h
+++ b/extensions/common/permissions/permissions_data.h
@@ -201,24 +201,21 @@ class PermissionsData {
   // page itself.
   bool CanCaptureVisiblePage(int tab_id, std::string* error) const;
 
-  const scoped_refptr<const PermissionSet>& active_permissions() const {
+  // Returns the tab permissions map.
+  TabPermissionsMap GetTabSpecificPermissionsMap() const;

[Jeffrey Yasskin, 2015/04/23 23:45:41]

I'm nervous about returning a std::map by value.

[Devlin, 2015/04/23 23:54:43]

Returning by reference is also Bad, because it's a map with refptrs - refptrs
which can be invalidated by setting tab permissions.  Is there a better way,
that's still safe, other than copying?

+
+  scoped_refptr<const PermissionSet> active_permissions() const {
     // We lock so that we can't also be setting the permissions while returning.
     base::AutoLock auto_lock(runtime_lock_);
     return active_permissions_unsafe_;
   }
 
-  const scoped_refptr<const PermissionSet>& withheld_permissions() const {
+  scoped_refptr<const PermissionSet> withheld_permissions() const {
     // We lock so that we can't also be setting the permissions while returning.
     base::AutoLock auto_lock(runtime_lock_);
     return withheld_permissions_unsafe_;
   }
 
-  const TabPermissionsMap& tab_specific_permissions() const {
-    // We lock so that we can't also be setting the permissions while returning.
-    base::AutoLock auto_lock(runtime_lock_);
-    return tab_specific_permissions_;
-  }
-
 #if defined(UNIT_TEST)
   scoped_refptr<const PermissionSet> GetTabSpecificPermissionsForTesting(
       int tab_id) const {