Use IsDeltaPayload instead of IsDelta.

Trying to resurrect the IsDelta in an earlier CL to avoid pollution of
Omaha rules turned out to be a wrong choice because R14 and R15 code
strictly expects IsDelta to be true even for full payloads. So
preserving IsDelta's semantics as-is and introducing IsDeltaPayload to
really convey the intended semantics: True if it's delta payload, False
if it's full payload.

BUG=chromium-os:37801
TEST=Updated unit tests. Works fine on ZGB with Omaha devserver.

Change-Id: I899b56be4dcbdcf1981f72d356d40a1e99fdf725
Reviewed-on: https://gerrit.chromium.org/gerrit/41181
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Jay Srinivasan <jaysri@chromium.org>
Tested-by: Jay Srinivasan <jaysri@chromium.org>
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index ece38b8..69d5895 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -88,6 +88,7 @@
       "ChromeOSVersion=\"" + display_version + "\" "
       "MoreInfo=\"" + more_info_url + "\" Prompt=\"" + prompt + "\" "
       "IsDelta=\"true\" "
+      "IsDeltaPayload=\"true\" "
       "MaxDaysToScatter=\"" + max_days_to_scatter + "\" "
       "sha256=\"" + hash + "\" "
       "needsadmin=\"" + needsadmin + "\" " +
@@ -732,6 +733,7 @@
       "ChromeOSVersion=\"10.2.3.4\" "
       "Prompt=\"false\" "
       "IsDelta=\"true\" "
+      "IsDeltaPayload=\"false\" "
       "sha256=\"lkq34j5345\" "
       "needsadmin=\"true\" "
       "/></actions></manifest></updatecheck></app></response>";