Support external context, heap and lcache (#1778)

JerryScript should support external context, heap and lcache,
so that it can have multiple instances and runtime configurable heap
size.

Related issue: 1746

JerryScript-DCO-1.0-Signed-off-by: Zidong Jiang zidong.jiang@intel.com

jerry-core/include/jerryscript-port.h

@@ -126,6 +126,18 @@ bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p);
  */
 double jerry_port_get_current_time (void);
 
+/**
+ * Get the current instance, which contains the current context, heap and other infomation.
+ * Each port should provide its own implementation of this interface.
+ *
+ *Note:
+ *    This port function will be called automatically by jerry-core
+ *    wnen JERRY_ENABLE_EXTERNAL_CONTEXT is defined. If not, this function will never be called.
+ *
+ * @return the pointer to the jerry instance.
+ */
+struct jerry_instance_t *jerry_port_get_current_instance (void);
+
 /**
  * @}
  */