Make sure abs-path gn labels have separate target_gen_dirs

tools/gn/substitution_writer_unittest.cc

 // Copyright 2014 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 <sstream>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/err.h"
 #include "tools/gn/escape.h"
 #include "tools/gn/substitution_list.h"
@@ skipping 142 matching lines @@
             GetAbsSubst("//foo/bar/baz.txt", SUBSTITUTION_SOURCE_GEN_DIR));
 
   EXPECT_EQ("obj/foo/bar",
             GetRelSubst("//foo/bar/baz.txt", SUBSTITUTION_SOURCE_OUT_DIR));
   EXPECT_EQ("//out/Debug/obj/foo/bar",
             GetAbsSubst("//foo/bar/baz.txt", SUBSTITUTION_SOURCE_OUT_DIR));
 
   // Operations on an absolute path.
   EXPECT_EQ("/baz.txt", GetRelSubst("/baz.txt", SUBSTITUTION_SOURCE));
   EXPECT_EQ("/.", GetRelSubst("/baz.txt", SUBSTITUTION_SOURCE_DIR));
-  EXPECT_EQ("gen", GetRelSubst("/baz.txt", SUBSTITUTION_SOURCE_GEN_DIR));
+  EXPECT_EQ("gen/ABS_PATH",
+            GetRelSubst("/baz.txt", SUBSTITUTION_SOURCE_GEN_DIR));
   EXPECT_EQ("obj/ABS_PATH",
             GetRelSubst("/baz.txt", SUBSTITUTION_SOURCE_OUT_DIR));
 #if defined(OS_WIN)
+  EXPECT_EQ("gen/ABS_PATH/C",
+            GetRelSubst("/C:/baz.txt", SUBSTITUTION_SOURCE_GEN_DIR));
   EXPECT_EQ("obj/ABS_PATH/C",
             GetRelSubst("/C:/baz.txt", SUBSTITUTION_SOURCE_OUT_DIR));
 #endif
 
   EXPECT_EQ(".",
             GetRelSubst("//baz.txt", SUBSTITUTION_SOURCE_ROOT_RELATIVE_DIR));
 
   #undef GetAbsSubst
   #undef GetRelSubst
 }
@@ skipping 77 matching lines @@
   // Test that we handle paths that end up in the root build dir properly
   // (no leading "./" or "/").
   SubstitutionPattern pattern;
   ASSERT_TRUE(pattern.Parse("{{root_out_dir}}/{{target_output_name}}.so",
                             nullptr, &err));
 
   OutputFile output = SubstitutionWriter::ApplyPatternToLinkerAsOutputFile(
       &target, tool, pattern);
   EXPECT_EQ("./libbaz.so", output.value());
 }