Do not cache an IOBuffer in AsyncResourceHandler if data_ is NULL.

chrome/browser/renderer_host/async_resource_handler.cc

Index: chrome/browser/renderer_host/async_resource_handler.cc
diff --git a/chrome/browser/renderer_host/async_resource_handler.cc b/chrome/browser/renderer_host/async_resource_handler.cc
index dfd1f56ed0d848d0a52ff776298332617a1d9432..95852bebf910c737f6998c6d7f4c8d2c7a380a1f 100644
--- a/chrome/browser/renderer_host/async_resource_handler.cc
+++ b/chrome/browser/renderer_host/async_resource_handler.cc
@@ -141,6 +141,8 @@ bool AsyncResourceHandler::OnResponseCompleted(
   if (g_spare_read_buffer) {
     read_buffer_ = NULL;
   } else if (read_buffer_.get()) {
+    // TODO(willchan): Remove after debugging bug 16371.
+    CHECK(read_buffer_->data());
     read_buffer_.swap(&g_spare_read_buffer);
   }
   return true;