--verify-predictable mode added for ensuring that GC behaves deterministically.

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 3b0af913fdf34f9ba6cbdc1efdb60b834d752bf6..e808788657f2bf967bbf1fde209cf604c4295fc0 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -41,6 +41,8 @@
 
     'v8_use_snapshot%': 'true',
 
+    'v8_enable_verify_predictable%': 0,
+
     # With post mortem support enabled, metadata is embedded into libv8 that
     # describes various parameters of the VM for use by debuggers. See
     # tools/gen-postmortem-metadata.py for details.
@@ -78,6 +80,9 @@
       ['v8_enable_verify_heap==1', {
         'defines': ['VERIFY_HEAP',],
       }],
+      ['v8_enable_verify_predictable==1', {
+        'defines': ['VERIFY_PREDICTABLE',],
+      }],
       ['v8_interpreted_regexp==1', {
         'defines': ['V8_INTERPRETED_REGEXP',],
       }],