data-fetcher: Discard really big data URLs.

mojo/fetcher/data_fetcher.cc

Index: mojo/fetcher/data_fetcher.cc
diff --git a/mojo/fetcher/data_fetcher.cc b/mojo/fetcher/data_fetcher.cc
index e785be7be9d074f41d927114d831e8e3abf199e4..51c25a8e8a73f8a74de61ae05e0cc61f4fd88a1f 100644
--- a/mojo/fetcher/data_fetcher.cc
+++ b/mojo/fetcher/data_fetcher.cc
@@ -18,6 +18,8 @@ namespace fetcher {
 
 ScopedDataPipeConsumerHandle CreateConsumerHandleForString(
     const std::string& data) {
+  if (data.size() > std::numeric_limits<uint32_t>::max())
+    return ScopedDataPipeConsumerHandle();
   uint32_t num_bytes = static_cast<uint32_t>(data.size());
   MojoCreateDataPipeOptions options;
   options.struct_size = sizeof(MojoCreateDataPipeOptions);