Fix ndb_cache* test failures in the -runtime tree.

Do not try to acquire structure_guard_mutex for the second time
when invalidating a table from send_result_to_client.


sql/sql_cache.cc:
  Do not try to acquire mutex when invalidating a table
  from send_result_to_client().
  A follow up patch for the patch for Bug#21074.
  Reuse code by moving locking-independent invalidation functionality
  into invalidate_table_internal.
sql/sql_cache.h:
  Add a new declaration.

sql/sql_cache.cc

@@ -1347,7 +1347,9 @@ def_week_frmt: %lu",
                    ("Handler require invalidation queries of %s.%s %lu-%lu",
                     table_list.db, table_list.alias,
                     (ulong) engine_data, (ulong) table->engine_data()));
-        invalidate_table(thd, (uchar *) table->db(), table->key_length());
+        invalidate_table_internal(thd,
+                                  (uchar *) table->db(),
+                                  table->key_length());
       }
       else
         thd->lex->safe_to_cache_query= 0;       // Don't try to cache this
@@ -2468,13 +2470,8 @@ void Query_cache::invalidate_table(THD *thd, uchar * key, uint32  key_length)
   m_cache_status= Query_cache::TABLE_FLUSH_IN_PROGRESS;
   STRUCT_UNLOCK(&structure_guard_mutex);
 
-  Query_cache_block *table_block=
-    (Query_cache_block*)hash_search(&tables, key, key_length);
-  if (query_cache_size > 0 && table_block)
-  {
-    Query_cache_block_table *list_root= table_block->table(0);
-    invalidate_query_block_list(thd, list_root);
-  }
+  if (query_cache_size > 0)
+    invalidate_table_internal(thd, key, key_length);
 
   STRUCT_LOCK(&structure_guard_mutex);
   m_cache_status= Query_cache::NO_FLUSH_IN_PROGRESS;
@@ -2488,6 +2485,26 @@ void Query_cache::invalidate_table(THD *thd, uchar * key, uint32  key_length)
 }
 
 
+/**
+  Try to locate and invalidate a table by name.
+  The caller must ensure that no other thread is trying to work with
+  the query cache when this function is executed.
+
+  @pre structure_guard_mutex is acquired or TABLE_FLUSH_IN_PROGRESS is set.
+*/
+
+void
+Query_cache::invalidate_table_internal(THD *thd, uchar *key, uint32 key_length)
+{
+  Query_cache_block *table_block=
+    (Query_cache_block*)hash_search(&tables, key, key_length);
+  if (table_block)
+  {
+    Query_cache_block_table *list_root= table_block->table(0);
+    invalidate_query_block_list(thd, list_root);
+  }
+}
+
 /**
   @brief Invalidate a linked list of query cache blocks.
 

sql/sql_cache.h

@@ -279,6 +279,7 @@ private:
   Cache_status m_cache_status;
 
   void free_query_internal(Query_cache_block *point);
+  void invalidate_table_internal(THD *thd, uchar *key, uint32 key_length);
 
 protected:
   /*