Absolute path fixes for gn.

tools/gn/filesystem_utils_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 "base/files/file_path.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/filesystem_utils.h"
@@ skipping 487 matching lines @@
   EXPECT_EQ("two/obj/",
             GetOutputDirForSourceDirAsOutputFile(
                 &other_settings, SourceDir("//")).value());
 
   EXPECT_EQ("//out/Debug/two/obj/foo/bar/",
             GetOutputDirForSourceDir(&other_settings,
                                      SourceDir("//foo/bar/")).value());
   EXPECT_EQ("two/obj/foo/bar/",
             GetOutputDirForSourceDirAsOutputFile(
                 &other_settings, SourceDir("//foo/bar/")).value());
+
+  // Absolute source path
+  EXPECT_EQ("//out/Debug/obj/ABS_PATH/abs/",
+            GetOutputDirForSourceDir(
+                &default_settings, SourceDir("/abs")).value());
+  EXPECT_EQ("obj/ABS_PATH/abs/",
+            GetOutputDirForSourceDirAsOutputFile(
+                &default_settings, SourceDir("/abs")).value());
 }
 
 TEST(FilesystemUtils, GetGenDirForSourceDir) {
   BuildSettings build_settings;
   build_settings.SetBuildDir(SourceDir("//out/Debug/"));
 
   // Test the default toolchain.
   Settings default_settings(&build_settings, "");
   EXPECT_EQ("//out/Debug/gen/",
             GetGenDirForSourceDir(
@@ skipping 49 matching lines @@
   EXPECT_EQ("gen/", GetToolchainGenDirAsOutputFile(&settings).value());
   EXPECT_EQ("//obj/",
             GetOutputDirForSourceDir(&settings, SourceDir("//")).value());
   EXPECT_EQ("obj/",
             GetOutputDirForSourceDirAsOutputFile(
                 &settings, SourceDir("//")).value());
   EXPECT_EQ("gen/",
             GetGenDirForSourceDirAsOutputFile(
                 &settings, SourceDir("//")).value());
 }