Add yasm to the GN build

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 61 matching lines @@
     "//third_party/mesa",
     "//third_party/ots",
     "//third_party/protobuf:protobuf_lite",
     "//third_party/qcms",
     "//third_party/re2",
     "//third_party/smhasher:cityhash",
     "//third_party/smhasher:murmurhash3",
     "//third_party/smhasher:pmurhash",
     "//third_party/WebKit/public:blink_headers",
     "//third_party/WebKit/Source/wtf",
+    "//third_party/yasm($host_toolchain)",
     "//third_party/zlib",
     "//third_party:jpeg",
     "//tools/gn",
     "//ui/aura",
     "//ui/accessibility",
     "//ui/base",
     "//ui/events",
     "//ui/gfx",
     "//ui/gl",
     "//ui/native_theme",
@@ skipping 51 matching lines @@
     ]
   }
 
   if (use_ozone) {
     deps += [
       "//ui/events/ozone:events_ozone",
       "//ui/events/ozone:events_ozone_evdev",
     ]
   }
 }