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

components/nacl/nacl_defines.gni

Index: components/nacl/nacl_defines.gni
diff --git a/components/nacl/nacl_defines.gni b/components/nacl/nacl_defines.gni
index 8d69b16af971934df3c4b617bc769e431d670368..a0b3da02894b9a55dc2e91a7fd087ee203679b91 100644
--- a/components/nacl/nacl_defines.gni
+++ b/components/nacl/nacl_defines.gni
@@ -35,22 +35,22 @@ if (is_android) {
   ]
 }
 
-if (cpu_arch == "x86") {
+if (current_cpu == "x86") {
   nacl_defines += [
     "NACL_BUILD_SUBARCH=32",
     "NACL_BUILD_ARCH=x86",
   ]
-} else if (cpu_arch == "x64") {
+} else if (current_cpu == "x64") {
   nacl_defines += [
     "NACL_BUILD_SUBARCH=64",
     "NACL_BUILD_ARCH=x86",
   ]
-} else if (cpu_arch == "arm") {
+} else if (current_cpu == "arm") {
   nacl_defines += [
     "NACL_BUILD_ARCH=arm",
     "NACL_BUILD_SUBARCH=32",
   ]
-} else if (cpu_arch == "mipsel") {
+} else if (current_cpu == "mipsel") {
   nacl_defines += [
     "NACL_BUILD_ARCH=mips",
     "NACL_BUILD_SUBARCH=32",