Build public cast_shell on x86 with GN.

chromecast/graphics/BUILD.gn

Index: chromecast/graphics/BUILD.gn
diff --git a/third_party/sudden_motion_sensor/BUILD.gn b/chromecast/graphics/BUILD.gn
similarity index 61%
copy from third_party/sudden_motion_sensor/BUILD.gn
copy to chromecast/graphics/BUILD.gn
index 26bdf4284cf7a8b204c21df7562d1deeb9d6f203..f07a87154354163b625be19de5dff4c5ca38b7c9 100644
--- a/third_party/sudden_motion_sensor/BUILD.gn
+++ b/chromecast/graphics/BUILD.gn
@@ -2,13 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("sudden_motion_sensor") {
+source_set("graphics") {
   sources = [
-    "sudden_motion_sensor_mac.cc",
-    "sudden_motion_sensor_mac.h",
+    "cast_screen.cc",
+    "cast_screen.h",
   ]
 
   deps = [
-    "//base",
+    "//ui/aura",
+    "//ui/gfx",
+    "//ui/gfx/geometry",
   ]
 }