Optionally use 31-bits SMI value for 64-bit system

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 3c6d25f7587c988b8aec9b81131781903f2e0c0b..bd8e538ff16434929274d441d54dcfc8a6f9d0dd 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -41,6 +41,8 @@
 
     'v8_enable_verify_heap%': 0,
 
+    'v8_use_31_bit_smi_value%': 0,
+
     'v8_use_snapshot%': 'true',
 
     # With post mortem support enabled, metadata is embedded into libv8 that
@@ -73,6 +75,9 @@
       ['v8_enable_verify_heap==1', {
         'defines': ['VERIFY_HEAP',],
       }],
+      ['v8_use_31_bit_smi_value==1', {
+        'defines': ['V8_USE_31_BIT_SMI_VALUE',],
+      }],
       ['v8_interpreted_regexp==1', {
         'defines': ['V8_INTERPRETED_REGEXP',],
       }],