update_engine: Barebone Omaha Request for DLC(s)

No need to maintain certain attributes for DLC update/install request to Omaha.

The list of uneccessary attributes for DLC AppIDs:
 - lang
 - fw_version
 - ec_version
 - requisition

BUG=chromium:1039898
TEST=FEATURES=test emerge-$B update_engine

Change-Id: I40efc3435d4c359470464f2dc6e32470cc629938
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/1992192
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
diff --git a/omaha_request_builder_xml.h b/omaha_request_builder_xml.h
index 495ddd7..488be8a 100644
--- a/omaha_request_builder_xml.h
+++ b/omaha_request_builder_xml.h
@@ -85,6 +85,7 @@
   std::string version;
   std::string product_components;
   bool skip_update;
+  bool is_dlc;
 };
 
 // Encodes XML entities in a given string. Input must be ASCII-7 valid. If
@@ -139,6 +140,9 @@
   std::string GetRequest() const override;
 
  private:
+  FRIEND_TEST(OmahaRequestBuilderXmlTest, PlatformGetAppTest);
+  FRIEND_TEST(OmahaRequestBuilderXmlTest, DlcGetAppTest);
+
   // Returns an XML that corresponds to the entire <os> node of the Omaha
   // request based on the member variables.
   std::string GetOs() const;