Try to resuscitate the builds needed to do official GN builds.

build/config/linux/BUILD.gn

Index: build/config/linux/BUILD.gn
diff --git a/build/config/linux/BUILD.gn b/build/config/linux/BUILD.gn
index 98d131e800006d6da7cec92fda4075ac81043f84..758f42a6164a935143689fb215835fe9a2e8ad27 100644
--- a/build/config/linux/BUILD.gn
+++ b/build/config/linux/BUILD.gn
@@ -118,8 +118,7 @@ if (!is_chromeos) {
   # These packages should _only_ be expected when building for a target.
   # If these extra checks are not run, gconf is required when building host
   # tools for a CrOS build.
-  if (current_toolchain == host_toolchain &&
-      host_toolchain == default_toolchain) {
+  if (current_toolchain == default_toolchain) {

[Chris Masone, 2014/11/04 23:33:16]

So, gconf is required only when compiling _target_ binaries for desktop Linux.
It is not actually required to compile host-side build tools. It's not available
in the CrOS build chroot because we don't need (or want) it.

The problem is that, when building host-side build tools as a part of building
for any other target, GN will also run through with is_linux=true and
is_chromeos=false...which means that  host tool compilation is mostly
indistinguishable from a desktop linux target build, even when you're building
for is_chromeos=true.

The case we'd really like to detect is "Currently building for the target, as
opposed to the host," which is a notion that GYP has but GN doesn't. The proxy
for this that we settled on is "There's no cross-compilation set up, so it's
probably fine to treat host and target builds the same for this".

Hence, checking that the toolchain currently in use is the host toolchain, which
is the same as the target (default) toolchain.

[brettw, 2014/11/04 23:47:52]

This is necessary for the 32-bit cross-compile, where the default toolchain is
32-bit, and the host is 64-bit. 

We use the default toolchain as the target toolchain, so I think the new
condition should satisfy your requirements as well.

[Chris Masone, 2014/11/05 00:53:31]

I definitely tried this first, and it didn't work in some case that I can no
longer reproduce :-)

If I run across it again, I'll start a thread explaining the problem to you guys
and we'll see what we can figure out.

     pkg_config("gconf") {
       packages = [ "gconf-2.0" ]
       defines = [ "USE_GCONF" ]