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

third_party/widevine/cdm/BUILD.gn

Index: third_party/widevine/cdm/BUILD.gn
diff --git a/third_party/widevine/cdm/BUILD.gn b/third_party/widevine/cdm/BUILD.gn
index b563eb4afa164d32e4703161a83418bbd92bbcc0..aa476af17422703c86f01da787b4fd61e3790642 100644
--- a/third_party/widevine/cdm/BUILD.gn
+++ b/third_party/widevine/cdm/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-widevine_arch = cpu_arch
+widevine_arch = current_cpu

[ddorwin, 2015/02/20 02:47:08]

The description says "current_cpu_arch", but multiple files appear to just use
"current_cpu".

[ddorwin, 2015/02/20 02:53:35]

What is the difference between current_cpu and target_cpu? It sounds like
neither are the host so either would work here.

[Dirk Pranke, 2015/02/20 03:00:26]

generally you want current_cpu (the cpu of the current toolchain).

Probably the only time you want to look at target_cpu instead is if you're
building something on one architecture (usually the host) but what you build
depends on what the target will ultimately be. V8 has this, where they
precompile some JS on the host but how they precompile it varies.

 if (widevine_arch == "x86") {
   widevine_arch = "ia32"
 }