GN: Don't write stamp files for one rule.

tools/gn/ninja_copy_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/ninja_copy_target_writer.h"
 #include "tools/gn/target.h"
@@ skipping 72 matching lines @@
       SubstitutionList::MakeForTest("//out/Debug/{{source_name_part}}.out");
   target.inputs().push_back(SourceFile("//foo/script.py"));
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
 
   std::ostringstream out;
   NinjaCopyTargetWriter writer(&target, out);
   writer.Run();
 
   const char expected_linux[] =
-      "build obj/foo/bar.inputdeps.stamp: stamp ../../foo/script.py\n"
-      "build input1.out: copy ../../foo/input1.txt || "
-          "obj/foo/bar.inputdeps.stamp\n"
+      "build input1.out: copy ../../foo/input1.txt || ../../foo/script.py\n"
       "\n"
       "build obj/foo/bar.stamp: stamp input1.out\n";
   std::string out_str = out.str();
   EXPECT_EQ(expected_linux, out_str);
 }