Add the concept of a source set to GN.

tools/gn/ninja_script_target_writer_unittest.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 <algorithm>
 #include <sstream>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/file_template.h"
 #include "tools/gn/ninja_script_target_writer.h"
@@ skipping 95 matching lines @@
 
     std::string out_str = out.str();
 #if defined(OS_WIN)
     std::replace(out_str.begin(), out_str.end(), '\\', '/');
 #endif
     EXPECT_EQ(expected_linux, out_str);
   }
 
   // Windows.
   {
+    // Note: we use forward slashes here so that the output will be the same on
+    // Linux and Windows.
+    setup.build_settings()->set_python_path(base::FilePath(FILE_PATH_LITERAL(
+        "C:/python/python.exe")));
     setup.settings()->set_target_os(Settings::WIN);
 
     std::ostringstream out;
     NinjaScriptTargetWriter writer(&target, out);
     writer.Run();
 
     // TODO(brettw) I think we'll need to worry about backslashes here
     // depending if we're on actual Windows or Linux pretending to be Windows.
     const char expected_win[] =
         "arch = environment.x86\n"
         "rule __foo_bar___rule\n"
-        "  command = $pythonpath gyp-win-tool action-wrapper $arch __foo_bar___rule.$unique_name.rsp\n"
+        "  command = C:/python/python.exe gyp-win-tool action-wrapper $arch __foo_bar___rule.$unique_name.rsp\n"
         "  description = CUSTOM //foo:bar()\n"
         "  restat = 1\n"
         "  rspfile = __foo_bar___rule.$unique_name.rsp\n"
-        "  rspfile_content = $pythonpath ../../foo/script.py -i ${source} \"--out=foo$ bar${source_name_part}.o\"\n"
+        "  rspfile_content = C:/python/python.exe ../../foo/script.py -i ${source} \"--out=foo$ bar${source_name_part}.o\"\n"
         "\n"
         "build input1.out: __foo_bar___rule../../foo/input1.txt | ../../foo/included.txt\n"
         "  unique_name = 0\n"
         "  source = ../../foo/input1.txt\n"
         "  source_name_part = input1\n"
         "build input2.out: __foo_bar___rule../../foo/input2.txt | ../../foo/included.txt\n"
         "  unique_name = 1\n"
         "  source = ../../foo/input2.txt\n"
         "  source_name_part = input2\n"
         "\n"
         "build obj/foo/bar.stamp: tc_stamp input1.out input2.out\n";
     std::string out_str = out.str();
 #if defined(OS_WIN)
     std::replace(out_str.begin(), out_str.end(), '\\', '/');
 #endif
     EXPECT_EQ(expected_win, out_str);
   }
 }