Accept absolute Windows paths without leading slash in GN commands

tools/gn/label_pattern_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 <stddef.h>
 
 #include "base/macros.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/err.h"
 #include "tools/gn/label_pattern.h"
@@ skipping 40 matching lines @@
     // Wildcards in invalid places.
     { "*foo*:bar", false, LabelPattern::MATCH, "", "", "" },
     { "foo*:*bar", false, LabelPattern::MATCH, "", "", "" },
     { "*foo:bar", false, LabelPattern::MATCH, "", "", "" },
     { "foo:bar*", false, LabelPattern::MATCH, "", "", "" },
     { "*:*", true, LabelPattern::RECURSIVE_DIRECTORY, "", "", "" },
     // Invalid toolchain stuff.
     { "//foo(//foo/bar:*)", false, LabelPattern::MATCH, "", "", "" },
     { "//foo/*(*)", false, LabelPattern::MATCH, "", "", "" },
     { "//foo(//bar", false, LabelPattern::MATCH, "", "", "" },
+    // Absolute paths.
+    { "/la/*", true, LabelPattern::RECURSIVE_DIRECTORY, "/la/", "", "" },
+    { "/la:bar", true, LabelPattern::MATCH, "/la/", "bar", "" },
+#if defined(OS_WIN)
+    { "/C:/la/*", true, LabelPattern::RECURSIVE_DIRECTORY, "/C:/la/", "", "" },
+    { "C:/la/*", true, LabelPattern::RECURSIVE_DIRECTORY, "/C:/la/", "", "" },
+    { "/C:/la:bar", true, LabelPattern::MATCH, "/C:/la/", "bar", "" },
+    { "C:/la:bar", true, LabelPattern::MATCH, "/C:/la/", "bar", "" },
+#endif
   };
 
   for (size_t i = 0; i < arraysize(cases); i++) {
     const PatternCase& cur = cases[i];
     Err err;
     LabelPattern result =
         LabelPattern::GetPattern(current_dir, Value(nullptr, cur.input), &err);
 
     EXPECT_EQ(cur.success, !err.has_error()) << i << " " << cur.input;
     EXPECT_EQ(cur.type, result.type()) << i << " " << cur.input;
     EXPECT_EQ(cur.dir, result.dir().value()) << i << " " << cur.input;
     EXPECT_EQ(cur.name, result.name()) << i << " " << cur.input;
     EXPECT_EQ(cur.toolchain, result.toolchain().GetUserVisibleName(false))
         << i << " " << cur.input;
   }
 }