allow config options to limit max size of decode

This is a practical concern to allow us to fail in a decoder instance
if the size of a file is bigger than we can reasonably handle.

Change-Id: I0446b5502b1f8a48408107648ff2a8d187dca393
diff --git a/test/video_source.h b/test/video_source.h
index 4250cb7..f7e31d4 100644
--- a/test/video_source.h
+++ b/test/video_source.h
@@ -127,6 +127,10 @@
 
   virtual unsigned int limit() const { return limit_; }
 
+  void set_limit(unsigned int limit) {
+    limit_ = limit;
+  }
+
   void SetSize(unsigned int width, unsigned int height) {
     if (width != width_ || height != height_) {
       vpx_img_free(img_);