Prop hashmap allocation strategy based on gc pattern is implemented. (#1429)

The algorithm is the following:
* introduced a counter variable, which value can be [0-4]
* if its value is 0, property hashmap allocation is enabled
* JMEM_FREE_UNUSED_MEMORY_SEVERITY_LOW -> decrease the counter
* JMEM_FREE_UNUSED_MEMORY_SEVERITY_HIGH -> increase the number
* if JMEM_FREE_UNUSED_MEMORY_SEVERITY_HIGH happens twice in a row increase the counter to 4

According to the measurements this algorithm provides better runtime results in low memory conditions.

JerryScript-DCO-1.0-Signed-off-by: István Kádár ikadar@inf.u-szeged.hu

jerry-core/ecma/base/ecma-property-hashmap.c

@@ -18,6 +18,7 @@
 #include "ecma-helpers.h"
 #include "ecma-property-hashmap.h"
 #include "jrt-libc-includes.h"
+#include "jcontext.h"
 
 /** \addtogroup ecma ECMA
  * @{
@@ -78,6 +79,11 @@ ecma_property_hashmap_create (ecma_object_t *object_p) /**< object */
   JERRY_ASSERT (ecma_get_property_list (object_p) != NULL);
   JERRY_ASSERT (ECMA_PROPERTY_IS_PROPERTY_PAIR (ecma_get_property_list (object_p)));
 
+  if (JERRY_CONTEXT (ecma_prop_hashmap_alloc_state) != ECMA_PROP_HASHMAP_ALLOC_ON)
+  {
+    return;
+  }
+
   uint32_t named_property_count = 0;
 
   ecma_property_header_t *prop_iter_p = ecma_get_property_list (object_p);