Work on GN iOS build.

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 "build/build_config.h"
 #include "tools/gn/variables.h"
 
 #if defined(OS_WIN)
@@ skipping 61 matching lines @@
 }
 
 void Args::AddArgOverrides(const Scope::KeyValueMap& overrides) {
   for (Scope::KeyValueMap::const_iterator i = overrides.begin();
        i != overrides.end(); ++i) {
     overrides_[i->first] = i->second;
     all_overrides_[i->first] = i->second;
   }
 }
 
+const Value* Args::GetArgOverride(const char* name) const {
+  Scope::KeyValueMap::const_iterator found =
+      all_overrides_.find(base::StringPiece(name));
+  if (found == all_overrides_.end())
+    return NULL;
+  return &found->second;
+}
+
 void Args::SetupRootScope(Scope* dest,
                           const Scope::KeyValueMap& toolchain_overrides) const {
   SetSystemVars(dest);
   ApplyOverrides(overrides_, dest);
   ApplyOverrides(toolchain_overrides, dest);
   SaveOverrideRecord(toolchain_overrides);
 }
 
 bool Args::DeclareArgs(const Scope::KeyValueMap& args,
                        Scope* scope_to_set,
@@ skipping 134 matching lines @@
   // Do not declare the build* variants since these shouldn't be changed.
   //
   // Mark these variables used so the build config file can override them
   // without geting a warning about overwriting an unused variable.
   declared_arguments_[variables::kOs] = os_val;
   declared_arguments_[variables::kCpuArch] = arch_val;
   dest->MarkUsed(variables::kCpuArch);
   dest->MarkUsed(variables::kOs);
 }
 
-
 void Args::ApplyOverrides(const Scope::KeyValueMap& values,
                           Scope* scope) const {
   for (Scope::KeyValueMap::const_iterator i = values.begin();
        i != values.end(); ++i)
     scope->SetValue(i->first, i->second, i->second.origin());
 }
 
 void Args::SaveOverrideRecord(const Scope::KeyValueMap& values) const {
   base::AutoLock lock(lock_);
   for (Scope::KeyValueMap::const_iterator i = values.begin();
        i != values.end(); ++i)
     all_overrides_[i->first] = i->second;
 }