Sketch of on demand snapshot generation for d8

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 6cb0c90cd8ccd793e57f86b81fb7fd48628e5be6..0d05f8474c8733cc484231c173448bc2eb59e4a0 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -62,6 +62,8 @@
     # Use external files for startup data blobs:
     # the JS builtins sources and the start snapshot.
     'v8_use_external_startup_data%': 0,
+
+    'v8_on_demand_snapshot%': 1,
   },
   'target_defaults': {
     'conditions': [
@@ -95,6 +97,9 @@
       ['v8_use_external_startup_data==1', {
         'defines': ['V8_USE_EXTERNAL_STARTUP_DATA',],
       }],
+      ['v8_on_demand_snapshot==1', {
+        'defines': ['V8_ON_DEMAND_SNAPSHOT',],
+      }],
     ],  # conditions
     'configurations': {
       'DebugBaseCommon': {