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/hardware_android.cc b/hardware_android.cc
index 80c7757..82f1b9a 100644
--- a/hardware_android.cc
+++ b/hardware_android.cc
@@ -121,6 +121,11 @@
   return GetProperty(kPropBootBaseband, "");
 }
 
+string HardwareAndroid::GetDeviceRequisition() const {
+  LOG(WARNING) << "STUB: Getting requisition is not supported.";
+  return "";
+}
+
 int HardwareAndroid::GetMinKernelKeyVersion() const {
   LOG(WARNING) << "STUB: No Kernel key version is available.";
   return -1;