Make rebase_path("//foo", "//foo") resolve to "." (not "../foo")

tools/gn/function_rebase_path_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 "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/test_with_scope.h"
 
@@ skipping 33 matching lines @@
 
   // Without a source root defined, we cannot move out of the source tree.
   EXPECT_EQ("../..", RebaseOne(scope, "../../..", "//out/Debug", "."));
 
   // Source-absolute input paths.
   EXPECT_EQ("./", RebaseOne(scope, "//", "//", "//"));
   EXPECT_EQ("foo", RebaseOne(scope, "//foo", "//", "//"));
   EXPECT_EQ("foo/", RebaseOne(scope, "//foo/", "//", "//"));
   EXPECT_EQ("../../foo/bar", RebaseOne(scope, "//foo/bar", "//out/Debug", "."));
   EXPECT_EQ("./", RebaseOne(scope, "//foo/", "//foo/", "//"));
-  // Thie one is technically correct but could be simplified to "." if
-  // necessary.
-  EXPECT_EQ("../foo", RebaseOne(scope, "//foo", "//foo", "//"));
+  EXPECT_EQ(".", RebaseOne(scope, "//foo", "//foo", "//"));
 
   // Test slash conversion.
   EXPECT_EQ("foo/bar", RebaseOne(scope, "foo/bar", ".", "."));
   EXPECT_EQ("foo/bar", RebaseOne(scope, "foo\\bar", ".", "."));
 
   // Test system path output.
 #if defined(OS_WIN)
   setup.build_settings()->SetRootPath(base::FilePath(L"C:/path/to/src"));
   EXPECT_EQ("C:/path/to/src", RebaseOne(scope, ".", "", "//"));
   EXPECT_EQ("C:/path/to/src/", RebaseOne(scope, "//", "", "//"));
@@ skipping 107 matching lines @@
 TEST(RebasePath, Errors) {
   TestWithScope setup;
 
   // No arg input should issue an error.
   Err err;
   std::vector<Value> args;
   FunctionCallNode function;
   Value ret = functions::RunRebasePath(setup.scope(), &function, args, &err);
   EXPECT_TRUE(err.has_error());
 }