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

third_party/libwebp/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/arm.gni")
 
 config("libwebp_config") {
   include_dirs = [ "." ]
 }
 
 use_dsp_neon =
-    cpu_arch == "arm64" || (cpu_arch == "arm" && arm_version >= 7 &&
-                            (arm_use_neon || arm_optionally_use_neon))
+    current_cpu == "arm64" || (current_cpu == "arm" && arm_version >= 7 &&
+                               (arm_use_neon || arm_optionally_use_neon))
 
 source_set("libwebp_dec") {
   sources = [
     "dec/alpha.c",
     "dec/buffer.c",
     "dec/frame.c",
     "dec/idec.c",
     "dec/io.c",
     "dec/quant.c",
     "dec/tree.c",
@@ skipping 71 matching lines @@
   source_set("libwebp_dsp_neon") {
     sources = [
       "dsp/dec_neon.c",
       "dsp/enc_neon.c",
       "dsp/lossless_neon.c",
       "dsp/upsampling_neon.c",
     ]
 
     include_dirs = [ "." ]
 
-    if (cpu_arch == "arm") {
+    if (current_cpu == "arm") {
       # behavior similar to *.c.neon in an Android.mk
       configs -= [ "//build/config/compiler:compiler_arm_fpu" ]
       cflags = [ "-mfpu=neon" ]
-    } else if (cpu_arch == "arm64") {
+    } else if (current_cpu == "arm64") {
       # avoid an ICE with gcc-4.9: b/15574841
       cflags = [ "-frename-registers" ]
     }
 
     # TODO(GYP):
     #        ['order_profiling != 0', {
     #          'target_conditions' : [
     #            ['_toolset=="target"', {
     #              'cflags!': [ '-finstrument-functions' ],
     #            }],
@@ skipping 60 matching lines @@
     ":libwebp_demux",
     ":libwebp_dsp",
     ":libwebp_enc",
     ":libwebp_utils",
   ]
   public_configs = [ ":libwebp_config" ]
   if (use_dsp_neon) {
     deps += [ ":libwebp_dsp_neon" ]
   }
 }