Allowing optional build of a WASM prototype behind a gyp define.

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 76bfa22a77cb47f4c48606a91ffb5d8fd8dedf7e..86b351105eed92e1f42b18e12184c1d9eeb5e27f 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -64,6 +64,9 @@
 
     # Set to 1 to enable DCHECKs in release builds.
     'dcheck_always_on%': 0,
+
+    # Set to 1 to enable building with wasm prototype.
+    'v8_wasm%': 0,
   },
   'target_defaults': {
     'conditions': [
@@ -103,6 +106,9 @@
       ['dcheck_always_on!=0', {
         'defines': ['DEBUG',],
       }],
+      ['v8_wasm!=0', {
+        'defines': ['V8_WASM',],
+      }],
     ],  # conditions
     'configurations': {
       'DebugBaseCommon': {