Update Chomium's build files to work w/ latest GN binaries.

media/BUILD.gn

Index: media/BUILD.gn
diff --git a/media/BUILD.gn b/media/BUILD.gn
index 1e7da3f215f9c69828c760f174a236bfadc5b833..9ab1e72970609758a2259446477f84c26f22becb 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -20,7 +20,7 @@ config("media_config") {
   if (!media_use_ffmpeg) {
     defines += [ "MEDIA_DISABLE_FFMPEG" ]
   }
-  if (cpu_arch == "arm" && arm_use_neon) {
+  if (current_cpu == "arm" && arm_use_neon) {
     defines += [ "USE_NEON" ]
   }
   if (use_pulseaudio) {
@@ -254,6 +254,7 @@ component("media") {
 
   configs += [
     ":media_config",
+
     # TODO(wolenetz): Fix size_t to int trunctaion in win64.
     # See http://crbug.com/171009
     "//build/config/compiler:no_size_t_to_int_warning",
@@ -297,7 +298,7 @@ component("media") {
     }
   }
 
-  if (cpu_arch == "arm" && arm_use_neon) {
+  if (current_cpu == "arm" && arm_use_neon) {
     defines += [ "USE_NEON" ]
   }
 
@@ -342,7 +343,7 @@ component("media") {
     }
   }
 
-  if (cpu_arch != "arm" && is_chromeos) {
+  if (current_cpu != "arm" && is_chromeos) {
     sources += [
       "filters/h264_bitstream_buffer.cc",
       "filters/h264_bitstream_buffer.h",
@@ -625,7 +626,7 @@ test("media_unittests") {
     ]
   }
 
-  if (cpu_arch != "arm" && is_chromeos) {
+  if (current_cpu != "arm" && is_chromeos) {
     sources += [ "filters/h264_bitstream_buffer_unittest.cc" ]
   }