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

content/common/BUILD.gn

Index: content/common/BUILD.gn
diff --git a/content/common/BUILD.gn b/content/common/BUILD.gn
index f738fc50bf2ff0feede75bdd285679ec0a40ddc3..b6f89eba3d8ec1ea8e24e1e9db14170267b84967 100644
--- a/content/common/BUILD.gn
+++ b/content/common/BUILD.gn
@@ -7,7 +7,7 @@ import("//build/config/ui.gni")
 import("//content/common/common.gni")
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
 
-if (is_chromeos && cpu_arch != "arm") {
+if (is_chromeos && current_cpu != "arm") {
   action("libva_generate_stubs") {
     extra_header = "gpu/media/va_stub_header.fragment"
 
@@ -243,7 +243,7 @@ source_set("common") {
     include_dirs += [ "//third_party/khronos" ]
     configs += [ "//build/config/linux:xcomposite" ]
 
-    if (cpu_arch != "arm" || !is_chromeos) {
+    if (current_cpu != "arm" || !is_chromeos) {
       sources += [
         "gpu/x_util.cc",
         "gpu/x_util.h",
@@ -284,7 +284,7 @@ source_set("common") {
     if (use_v4l2_codec) {
       defines += [ "USE_V4L2_CODEC" ]
     }
-    if (cpu_arch == "arm" || (use_ozone && use_v4l2_codec)) {
+    if (current_cpu == "arm" || (use_ozone && use_v4l2_codec)) {
       sources += [
         "gpu/media/generic_v4l2_video_device.cc",
         "gpu/media/generic_v4l2_video_device.h",
@@ -301,14 +301,14 @@ source_set("common") {
         "EGL",
         "GLESv2",
       ]
-      if (cpu_arch == "arm") {
+      if (current_cpu == "arm") {
         sources += [
           "gpu/media/tegra_v4l2_video_device.cc",
           "gpu/media/tegra_v4l2_video_device.h",
         ]
       }
     }
-    if (cpu_arch != "arm") {
+    if (current_cpu != "arm") {
       sources += [
                    "gpu/media/va_surface.h",
                    "gpu/media/vaapi_h264_decoder.cc",