Normalize paths in GN.

tools/gn/source_file_unittest.cc

+// Copyright 2015 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 "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/source_file.h"
+
+// The SourceFile object should normalize the input passed to the constructor.
+// The normalizer unit test checks for all the weird edge cases for normalizing
+// so here just check that it gets called.
+TEST(SourceFile, Normalize) {
+  SourceFile a("//foo/../bar.cc");
+  EXPECT_EQ("//bar.cc", a.value());
+
+  std::string b_str("//foo/././../bar.cc");
+  SourceFile b(SourceFile::SwapIn(), &b_str);
+  EXPECT_TRUE(b_str.empty());  // Should have been swapped in.
+  EXPECT_EQ("//bar.cc", b.value());
+}