Allow specific files and multiple inputs for picture testing tools.

Changed the render_pictures, bench_pictures and test_pictures.py so that multiple inputs can be given. Furthermore, specific files can also be specified.

Unit tests have also been added for picture_utils.cpp.

Review URL: https://codereview.appspot.com/6345054

git-svn-id: http://skia.googlecode.com/svn/trunk@4486 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/picture_utils.h b/tools/picture_utils.h
index 21651cd..18efcb7 100644
--- a/tools/picture_utils.h
+++ b/tools/picture_utils.h
@@ -19,6 +19,12 @@
     // forward slash into path.
     void make_filepath(SkString* path, const char* dir, const SkString& name);
 
+    // Returns the last part of the path (file name or leaf directory name)
+    //
+    // This basically just looks for a foward slash or backslash (windows
+    // only)
+    void get_basename(SkString* basename, const SkString& path);
+
     // Prepares the bitmap so that it can be written.
     //
     // Specifically, it configures the bitmap, allocates pixels and then