Add a histogram for size of the memory used by redirect chain.

url/gurl.h

Index: url/gurl.h
diff --git a/url/gurl.h b/url/gurl.h
index b8632b45e91007c52601bd14be913bd2cb876fcd..cf15ad96a3995cd91273c37fd04717f60e1d4277 100644
--- a/url/gurl.h
+++ b/url/gurl.h
@@ -362,6 +362,9 @@ class URL_EXPORT GURL {
     return inner_url_.get();
   }
 
+  // Returns approximate size of the memory taken by the instance.
+  size_t Bytesize() const;
+
  private:
   // Variant of the string parsing constructor that allows the caller to elect
   // retain trailing whitespace, if any, on the passed URL spec but only  if the