Introducing 'try to give memory back' callback for heap allocator to use upon allocation request that can not be satisfied by the allocator.

src/libecmaobjects/ecma-gc.h

@@ -24,6 +24,7 @@
 #define ECMA_GC_H
 
 #include "ecma-globals.h"
+#include "mem-allocator.h"
 
 /**
  * GC generation identifier
@@ -43,6 +44,7 @@ extern void ecma_deref_object (ecma_object_t *object_p);
 extern void ecma_gc_update_may_ref_younger_object_flag_by_value (ecma_object_t *obj_p, ecma_value_t value);
 extern void ecma_gc_update_may_ref_younger_object_flag_by_object (ecma_object_t *obj_p, ecma_object_t *ref_obj_p);
 extern void ecma_gc_run (ecma_gc_gen_t max_gen_to_collect);
+extern void ecma_try_to_give_back_some_memory (mem_try_give_memory_back_severity_t severity);
 
 #endif /* !ECMA_GC_H */