[gn] Add swarming support

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 05bcec911429f3278157d43f0a4151c6ef491863..56a65e4fce660646dc13fc6e55ebe62a1aad3061 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -12,19 +12,12 @@ if (is_android) {
 }
 
 import("gni/v8.gni")
+import("gni/isolate.gni")
 import("//build_overrides/v8.gni")
 
 import("snapshot_toolchain.gni")
 
 declare_args() {
-  # Enable the snapshot feature, for fast context creation.
-  # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
-  v8_use_snapshot = true
-
-  # Use external files for startup data blobs:
-  # the JS builtins sources and the start snapshot.
-  v8_use_external_startup_data = !is_ios
-
   # Sets -DVERIFY_HEAP.
   v8_enable_verify_heap = false
 
@@ -2148,6 +2141,14 @@ executable("d8") {
   }
 }
 
+v8_isolate_run("d8") {

[Michael Achenbach, 2016/06/02 14:23:57]

This ports https://cs.chromium.org/chromium/src/v8/src/d8.gyp?l=142

Only d8 for now to test this on the staging bot. Others in follow up CLs.

+  deps = [
+    ":d8",
+  ]
+
+  isolate = "//src/d8.isolate"
+}
+
 if (want_v8_shell) {
   executable("v8_shell") {
     sources = [