Set default updater URL and version per platform.

Chrome OS and Brillo devices require different production update URL
and updater string ID sent to Omaha. This patch moves these constants
to a platform-dependent file with the definition of the constants.

Bug: brillo:587,brillo:588
Test: FEATURES=test emerge-link update_engine; `mma`; deployed on a dragonboard.

Change-Id: Ibe3b30c32c2fb2caf3ed10a4198272dc13a44d12
diff --git a/omaha_request_action.cc b/omaha_request_action.cc
index 2be66af..05d950f 100644
--- a/omaha_request_action.cc
+++ b/omaha_request_action.cc
@@ -40,6 +40,7 @@
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/p2p_manager.h"
 #include "update_engine/payload_state_interface.h"
+#include "update_engine/platform_constants.h"
 #include "update_engine/prefs_interface.h"
 #include "update_engine/utils.h"
 
@@ -71,9 +72,9 @@
 static const char* kTagDisableP2PForSharing = "DisableP2PForSharing";
 static const char* kTagPublicKeyRsa = "PublicKeyRsa";
 
-namespace {
+static const char* kOmahaUpdaterVersion = "0.1.0.0";
 
-static const char* const kGupdateVersion = "ChromeOSUpdateEngine-0.1.0.0";
+namespace {
 
 // Returns an XML ping element attribute assignment with attribute
 // |name| and value |ping_days| if |ping_days| has a value that needs
@@ -289,12 +290,15 @@
   string install_source = base::StringPrintf("installsource=\"%s\" ",
       (params->interactive() ? "ondemandupdate" : "scheduler"));
 
+  string updater_version = XmlEncodeWithDefault(
+      base::StringPrintf("%s-%s",
+                         constants::kOmahaUpdaterID,
+                         kOmahaUpdaterVersion), "");
   string request_xml =
       "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
       "<request protocol=\"3.0\" " + (
-          "version=\"" + XmlEncodeWithDefault(kGupdateVersion, "") + "\" "
-          "updaterversion=\"" + XmlEncodeWithDefault(kGupdateVersion,
-                                                     "") + "\" " +
+          "version=\"" + updater_version + "\" "
+          "updaterversion=\"" + updater_version + "\" " +
           install_source +
           "ismachine=\"1\">\n") +
       os_xml +