Work on GN toolchain definitions and build

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 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.
 
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
 #
 # This block lists input arguments to the build, along with their default
 # values. GN requires listing them explicitly so it can validate input and have
@@ skipping 100 matching lines @@
   is_ios = false
   is_linux = false
   is_mac = true
   is_nacl = false
   is_posix = true
   is_win = false
   if (!is_clang) {
     is_clang = true  # Always use clang on Mac.
   }
 } else if (os == "android") {
-  is_android = false
+  is_android = true
   is_chromeos = false
   is_ios = false
   is_linux = true
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (os == "chromeos") {
   is_android = false
   is_chromeos = true
@@ skipping 274 matching lines @@
 # ==============================================================================
 # TOOLCHAIN SETUP
 # ==============================================================================
 #
 # Here we set the default toolchain, as well as the variable host_toolchain
 # which will identify the toolchain corresponding to the local system when
 # doing cross-compiles. When not cross-compiling, this will be the same as the
 # default toolchain.
 
 if (is_win) {
+  # TODO(brettw) name the toolchains the same as cpu_arch as with Linux below
+  # to eliminate these conditionals.
   if (build_cpu_arch == "x64") {
     host_toolchain = "//build/toolchain/win:64"
   } else if (build_cpu_arch == "x86") {
     host_toolchain = "//build/toolchain/win:32"
   }
 
   if (cpu_arch == "x64") {
     set_default_toolchain("//build/toolchain/win:64")
   } else if (cpu_arch == "x86") {
     set_default_toolchain("//build/toolchain/win:32")
   }
+} else if (is_android) {
+  host_toolchain = "//build/toolchain/linux:$build_cpu_arch"
+  set_default_toolchain("//build/toolchain/android:$cpu_arch")
 } else if (is_linux) {
-  if (build_cpu_arch == "arm") {
-    host_toolchain = "//build/toolchain/linux:arm"
-  } else if (build_cpu_arch == "x86") {
-    host_toolchain = "//build/toolchain/linux:32"
-  } else if (build_cpu_arch == "x64") {
-    host_toolchain = "//build/toolchain/linux:64"
-  }
-
-  if (build_cpu_arch == "arm") {
-    set_default_toolchain("//build/toolchain/linux:arm")
-  } else if (build_cpu_arch == "x86") {
-    set_default_toolchain("//build/toolchain/linux:32")
-  } else if (build_cpu_arch == "x64") {
-    set_default_toolchain("//build/toolchain/linux:64")
-  }
+  host_toolchain = "//build/toolchain/linux:$build_cpu_arch"
+  set_default_toolchain("//build/toolchain/linux:$cpu_arch")
 } else if (is_mac || is_ios) {
   host_toolchain = "//build/toolchain/mac:clang"
   set_default_toolchain(host_toolchain)
 }