Adding ecma-string's hash to ecma_string_t.

src/libecmaobjects/ecma-globals.h

@@ -740,6 +740,16 @@ typedef enum
   ECMA_MAGIC_STRING__COUNT /**< number of magic strings */
 } ecma_magic_string_id_t;
 
+/**
+ * ECMA string hash
+ */
+typedef uint16_t ecma_string_hash_t;
+
+/**
+ * Number of string's last characters to use for hash calculation
+ */
+#define ECMA_STRING_HASH_LAST_CHARS_COUNT (2)
+
 /**
  * ECMA string-value descriptor
  */
@@ -755,8 +765,8 @@ typedef struct
     * in a stack variable (not in the heap) */
   unsigned int is_stack_var : 1;
 
-  /** Padding */
-  ecma_length_t padding;
+  /** Hash of the string (calculated from two last characters of the string) */
+  ecma_string_hash_t hash;
 
   /**
    * Actual data or identifier of it's place in container (depending on 'container' field)