GN: don't write separate files for non-binary targets

tools/gn/toolchain.h

 // 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.
 
 #ifndef TOOLS_GN_TOOLCHAIN_H_
 #define TOOLS_GN_TOOLCHAIN_H_
 
 #include <memory>
 
 #include "base/logging.h"
@@ skipping 48 matching lines @@
   static const char* kToolAsm;
   static const char* kToolAlink;
   static const char* kToolSolink;
   static const char* kToolSolinkModule;
   static const char* kToolLink;
   static const char* kToolStamp;
   static const char* kToolCopy;
   static const char* kToolCopyBundleData;
   static const char* kToolCompileXCAssets;
 
+  // The Settings of an Item is always the context in which the Item was
+  // defined. For a toolchain this is confusing because this is NOT the
+  // settings object that applies to the things in the toolchain.
+  //
+  // To get the Settings object corresponding to objects loaded in the context
+  // of this toolchain (probably what you want instead), see
+  // Loader::GetToolchainSettings(). Many toolchain objects may be created in a
+  // given build, but only a few might be used, and the Loader is in charge of
+  // this process.
   Toolchain(const Settings* settings, const Label& label);
   ~Toolchain() override;
 
   // Item overrides.
   Toolchain* AsToolchain() override;
   const Toolchain* AsToolchain() const override;
 
   // Returns TYPE_NONE on failure.
   static ToolType ToolNameToType(const base::StringPiece& str);
   static std::string ToolTypeToName(ToolType type);
@@ skipping 49 matching lines @@
   bool setup_complete_;
 
   // Substitutions used by the tools in this toolchain.
   SubstitutionBits substitution_bits_;
 
   LabelTargetVector deps_;
   Scope::KeyValueMap args_;
 };
 
 #endif  // TOOLS_GN_TOOLCHAIN_H_