Counting hits for queries in query cache.

Added hit_count field to Query_cache_query and methods to get and increment it.
The counter is incremented when query results are read from query cache.

sql/sql_cache.cc

@@ -961,7 +961,7 @@ inline void Query_cache_query::unlock_reading()
 void Query_cache_query::init_n_lock()
 {
   DBUG_ENTER("Query_cache_query::init_n_lock");
-  res=0; wri = 0; len = 0; ready= 0;
+  res=0; wri = 0; len = 0; ready= 0; hit_count = 0;
   mysql_rwlock_init(key_rwlock_query_cache_query_lock, &lock);
   lock_writing();
   DBUG_PRINT("qcache", ("inited & locked query for block 0x%lx",
@@ -2142,6 +2142,7 @@ def_week_frmt: %lu, in_trans: %d, autocommit: %d",
   }
   move_to_query_list_end(query_block);
   hits++;
+  query->increment_hits();
   unlock();
 
   /*

sql/sql_cache.h

@@ -159,6 +159,7 @@ struct Query_cache_query
   unsigned int last_pkt_nr;
   uint8 tbls_type;
   uint8 ready;
+  ulonglong hit_count;
 
   Query_cache_query() {}                      /* Remove gcc warning */
   inline void init_n_lock();
@@ -184,6 +185,8 @@ struct Query_cache_query
   */
   inline void set_results_ready()          { ready= 1; }
   inline bool is_results_ready()           { return ready; }
+  inline void increment_hits() { hit_count++; }
+  inline ulong hits() { return hit_count; }
   void lock_writing();
   void lock_reading();
   bool try_lock_writing();