Add CHECKs to help debug crashes exposed by adding a member to IPC::Message::Header.

content/child/resource_dispatcher.cc

Index: content/child/resource_dispatcher.cc
diff --git a/content/child/resource_dispatcher.cc b/content/child/resource_dispatcher.cc
index aeb1cbebc66081a825d767c136866c04d3bbe4fd..baf79aece718232c05fc097c35ff775116d35817 100644
--- a/content/child/resource_dispatcher.cc
+++ b/content/child/resource_dispatcher.cc
@@ -221,6 +221,8 @@ void ResourceDispatcher::OnReceivedData(int request_id,
   if (request_info && data_length > 0) {
     CHECK(base::SharedMemory::IsHandleValid(request_info->buffer->handle()));
     CHECK_GE(request_info->buffer_size, data_offset + data_length);
+    // TODO(erikchen): Temporary debugging for http://crbug.com/527588.
+    CHECK_LE(data_offset, 512 * 1024);
 
     // Ensure that the SHM buffer remains valid for the duration of this scope.
     // It is possible for Cancel() to be called before we exit this scope.