[Bindings] Create and use V8 context snapshots

tools/blink_v8_snapshot/BUILD.gn

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+group("blink_v8_snapshot") {
+  public_deps = [
+    ":generate_blink_v8_snapshot",
+  ]
+}
+
+action("generate_blink_v8_snapshot") {
+  script = "run.py"
+  output_file = "$root_out_dir/blink_v8_snapshot.bin"
+  output_path = rebase_path(output_file, root_build_dir)
+
+  args = [
+    "./" + rebase_path(
+            get_label_info(":blink_v8_snapshot_generator($host_toolchain)",
+                           "root_out_dir") + "/blink_v8_snapshot_generator",
+            root_build_dir),
+    "--output_file=$output_path",
+  ]
+
+  outputs = [
+    output_file,
+  ]
+
+  deps = [
+    ":blink_v8_snapshot_generator($host_toolchain)",
+  ]
+}
+
+# This config disables a link time optimization "ICF", which may merge different
+# functions into one if the function signature and body of them are identical.
+config("disable_icf") {
+  visibility = [ ":*" ]  # Only targets in this file can depend on this.
+  if (is_win) {
+    ldflags = [ "/OPT:NOICF" ]
+  } else if (is_posix && !is_mac) {
+    ldflags = [ "-Wl,--icf=none" ]
+  }
+}
+
+executable("blink_v8_snapshot_generator") {
+  sources = [
+    "blink_v8_snapshot_generator.cc",
+  ]
+
+  deps = [
+    "//gin:gin",
+    "//mojo/edk/system:system",
+    "//third_party/WebKit/public:blink",
+    "//v8",
+  ]
+
+  # Link time optimization "ICF" breaks 1:1 mappings of the external references
+  # for V8 snapshot. So, we disable it while taking a V8 snapshot.
+  configs += [
+    "//v8:external_startup_data",
+    ":disable_icf",
+  ]
+}