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_unittest.cc b/omaha_request_params_unittest.cc
index 7332431..bfcbc32 100644
--- a/omaha_request_params_unittest.cc
+++ b/omaha_request_params_unittest.cc
@@ -258,4 +258,8 @@
   EXPECT_TRUE(params_.CollectECFWVersions());
 }
 
+TEST_F(OmahaRequestParamsTest, RequisitionIsSetTest) {
+  EXPECT_TRUE(params_.Init("", "", false));
+  EXPECT_EQ("fake_requisition", params_.device_requisition());
+}
 }  // namespace chromeos_update_engine