Make WebDataConsumerHandleImpl return OK while zero-length reading of closed pipe.

content/child/web_data_consumer_handle_impl.cc

Index: content/child/web_data_consumer_handle_impl.cc
diff --git a/content/child/web_data_consumer_handle_impl.cc b/content/child/web_data_consumer_handle_impl.cc
index c111cca36035cb5863d525749d0a6bbf71930bf9..efb4f47084592ab01ab4b192644fc6aadc9df078 100644
--- a/content/child/web_data_consumer_handle_impl.cc
+++ b/content/child/web_data_consumer_handle_impl.cc
@@ -63,6 +63,12 @@ Result WebDataConsumerHandleImpl::ReaderImpl::read(void* data,
   if (rv == MOJO_RESULT_OK)
     *read_size = size_to_pass;
 
+  // Even if there is unread data available, mojo::ReadDataRaw() returns
+  // FAILED_PRECONDITION when |size| is 0 and the producer handle was closed.
+  // But in this case, WebDataConsumerHandle::Reader::read() must return Ok.
+  if (!size && rv == MOJO_RESULT_FAILED_PRECONDITION)
+    return Ok;
+
   return HandleReadResult(rv);
 }