update_engine: add chrome os device requisition to the omaha request

Requisition type is not currently sent to Omaha and is thus unavailable
for AU rules. This adds a requisition attribute to the <app> if the
device has a requisition type. Currently, the types may be one of
remora, shark, or rialto.

TEST=unittest
BUG=b:132014633,b:133324571

Change-Id: I0e53d3a5749da4cbb95ce73cff35191066339009
Reviewed-on: https://chromium-review.googlesource.com/1604218
Commit-Ready: Matthew Ziegelbaum <ziegs@chromium.org>
Tested-by: Matthew Ziegelbaum <ziegs@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/omaha_request_params.cc b/omaha_request_params.cc
index 8c410f1..70867a3 100644
--- a/omaha_request_params.cc
+++ b/omaha_request_params.cc
@@ -95,6 +95,7 @@
     fw_version_ = system_state_->hardware()->GetFirmwareVersion();
     ec_version_ = system_state_->hardware()->GetECVersion();
   }
+  device_requisition_ = system_state_->hardware()->GetDeviceRequisition();
 
   if (image_props_.current_channel == mutable_image_props_.target_channel) {
     // deltas are only okay if the /.nodelta file does not exist.  if we don't