fix skpdiff viewer bug when using relative paths

BUG=skia:1463
R=djsollen@google.com

Review URL: https://codereview.chromium.org/21601002

git-svn-id: http://skia.googlecode.com/svn/trunk@10515 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skpdiff/skpdiff_util.h b/tools/skpdiff/skpdiff_util.h
index 9df1bc0..8750bf6 100644
--- a/tools/skpdiff/skpdiff_util.h
+++ b/tools/skpdiff/skpdiff_util.h
@@ -49,5 +49,12 @@
  */
 bool glob_files(const char globPattern[], SkTArray<SkString>* entries);
 
+/**
+ * Gets the absolute version of the given path.
+ * @param  path The absolute or relative path to expand
+ * @return      The absolute path of the given path on success, or an empty string on failure.
+ */
+SkString get_absolute_path(const SkString& path);
+
 
 #endif