Update from https://crrev.com/317530

build/toolchain/win/BUILD.gn

Index: build/toolchain/win/BUILD.gn
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index b8f87e7157acc39d0fc8aa453c1861fd4e2c083f..e9461a4644b4f5a88174cecb1216209cf04b7dcd 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -31,7 +31,7 @@ toolchain_data = exec_script("setup_toolchain.py",
                                gyp_win_tool_path,
                                windows_sdk_path,
                                visual_studio_runtime_dirs,
-                               cpu_arch,
+                               current_cpu,
                              ],
                              "scope")
 
@@ -43,7 +43,7 @@ if (vc_bin_dir == "") {
 concurrent_links = exec_script("../get_concurrent_links.py", [], "value")
 
 # Parameters:
-#  cpu_arch: cpu_arch to pass as a build arg
+#  current_cpu: current_cpu to pass as a build arg
 #  environment: File name of environment file.
 template("msvc_toolchain") {
   if (defined(invoker.concurrent_links)) {
@@ -62,7 +62,7 @@ template("msvc_toolchain") {
                 "copy_dlls",
                 rebase_path(root_build_dir),
                 configuration,
-                invoker.cpu_arch,
+                invoker.current_cpu,
               ])
 
   if (use_goma) {
@@ -200,7 +200,10 @@ template("msvc_toolchain") {
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     toolchain_args() {
-      cpu_arch = invoker.cpu_arch
+      current_cpu = invoker.current_cpu
+
+      # TODO(dpranke): cpu_arch is here for backwards compatibility.
+      cpu_arch = current_cpu
     }
   }
 }
@@ -209,16 +212,18 @@ template("msvc_toolchain") {
 # get it sorted out how we want to support them both in a single build.
 # Right now only one of these can be enabled at a time because the
 # runtime libraries get copied to root_build_dir and would collide.
-if (cpu_arch == "x86") {
+if (current_cpu == "x86") {
   msvc_toolchain("32") {
     environment = "environment.x86"
-    cpu_arch = "x86"
+
+    current_cpu = "x86"
   }
 }
 
-if (cpu_arch == "x64") {
+if (current_cpu == "x64") {
   msvc_toolchain("64") {
     environment = "environment.x64"
-    cpu_arch = "x64"
+
+    current_cpu = "x64"
   }
 }