Add path utils, plus a test for it.

include/utils/SkOSPathUtils.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+class SkString;
+
+/**
+ * Assembles rootPath and relativePath into a single path, like this:
+ * rootPath/relativePath
+ *
+ * Uses SkPATH_SEPARATOR, to work on all platforms.
+ */
+SkString SkPathJoin(const char *rootPath, const char *relativePath);
+
+/**
+ *  Return the name of the file, ignoring the directory structure.
+ *  Behaves like python's os.path.basename. If the fullPath is
+ *  /dir/subdir/, an empty string is returned.
+ *  @param fullPath Full path to the file.
+ *  @return SkString The basename of the file - anything beyond the
+ *      final slash, or the full name if there is no slash.
+ */
+SkString SkBasename(const char* fullPath);