Add gn dependency on v8 back in

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 46 matching lines @@
     "//third_party/zlib",
     "//third_party:jpeg",
     "//tools/gn",
     "//ui/base:ui_base",
     "//ui/events",
     "//ui/gfx",
     "//ui/resources",
     "//ui/strings",
     "//ui/surface",
     "//url",
+    "//v8:mksnapshot",
   ]
 
   if (is_linux) {
     deps += [
       "//third_party/freetype2",
     ]
   }
 
   if (is_android) {
     deps -= [
       "//components/os_crypt",
       "//crypto",
       "//gpu/command_buffer/client",  # Needs Skia.
       "//net",
       "//skia",  # Needs some ARM stuff
       "//third_party/libusb",
       "//third_party/WebKit/Source/wtf",  # TODO(brettw) re-enable for Android.
       "//tools/gn",
       "//ui/base:ui_base",
       "//ui/events",
       "//ui/gfx",
       "//ui/surface",  # TODO(brettw): Skia does not build on Android yet.
                        # Re-enable this when skia is fixed.
     ]
   }
 }