Add path utils, plus a test for it.

include/utils/SkOSPathUtils.h

+/*
+ * Copyright 2013 Google Inc.

[epoger, 2013/05/22 17:33:58]

You might want to get Mike's blessing before adding this file to include/ .  He
may want to keep it private, I dunno.

And if we make it public, is there some SK_API macro we need to use in the
definitions?

[scroggo, 2013/05/23 15:29:33]

I believe we only need to add SK_API if code outside of Skia is using it.

+ *
+ * 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.
+ *  Does not create a new string.
+ *  @param fullPath Full path to the file.
+ *  @return string The basename of the file - anything beyond the
+ *      final slash, or the full name if there is no slash.
+ */
+const char* SkBasename(const char* fullPath);