[MIPS] Fix gn_unittests LoaderTest.Foo test

tools/gn/args.cc

 // 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.
 
 #include "tools/gn/args.h"
 
 #include "base/sys_info.h"
 #include "build/build_config.h"
 #include "tools/gn/variables.h"
 
@@ skipping 227 matching lines @@
 #elif defined(OS_ANDROID)
   os = "android";
 #else
   #error Unknown OS type.
 #endif
 
   // Host architecture.
   static const char kX86[] = "x86";
   static const char kX64[] = "x64";
   static const char kArm[] = "arm";
+  static const char kMips[] = "mipsel";
   const char* arch = nullptr;
 
   // Set the host CPU architecture based on the underlying OS, not
   // whatever the current bit-tedness of the GN binary is.
   std::string os_arch = base::SysInfo::OperatingSystemArchitecture();
   if (os_arch == "x86")
     arch = kX86;
   else if (os_arch == "x86_64")
     arch = kX64;
   else if (os_arch.substr(3) == "arm")
     arch = kArm;
+  else if (os_arch == "mips")
+    arch = kMips;
   else
     CHECK(false) << "OS architecture not handled.";
 
   // Save the OS and architecture as build arguments that are implicitly
   // declared. This is so they can be overridden in a toolchain build args
   // override, and so that they will appear in the "gn args" output.
   Value empty_string(nullptr, std::string());
 
   Value os_val(nullptr, std::string(os));
   dest->SetValue(variables::kHostOs, os_val, nullptr);
@@ skipping 35 matching lines @@
   lock_.AssertAcquired();
   for (const auto& val : values)
     all_overrides_[val.first] = val.second;
 }
 
 Scope::KeyValueMap& Args::DeclaredArgumentsForToolchainLocked(
     Scope* scope) const {
   lock_.AssertAcquired();
   return declared_arguments_per_toolchain_[scope->settings()];
 }