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/sample_omaha_v3_response.xml b/sample_omaha_v3_response.xml
index cb3bff7..abba523 100644
--- a/sample_omaha_v3_response.xml
+++ b/sample_omaha_v3_response.xml
@@ -11,7 +11,7 @@
         </packages>
         <actions>
           <action event="update" run="chromeos_3095.0.0_x86-zgb_canary-channel_full_mp-v2.bin-df37843370ddf1e3819a2afeaa934faa.signed"/>
-          <action ChromeOSVersion="3095.0.0" ChromeVersion="24.0.1307.0" IsDelta="true" MaxDaysToScatter="14" MetadataSignatureRsa="xXrO/LahHlKk3YmqEf1qE0PN587Sc2IJV+FN7J7x1h49waNQIy/QwYO4LaOySgETe5JZXtkAEzzqakfJwxQ2pVfzj1GkExwjd5LTn1He2GvA73B8fKbS4bfP7dbUFwD5039xCwf1U2gezFViOiOPiVURx/pEsdhv+Cqx/3HbjIuj5au2dooSyDxLC5AnODzAKyYfAcjMuiLON+9SqmctJW+VjzdY9SbJAnkH2qqVjFyBKAXsYT+hOTIJ3MJpg8OSVxMMtGB99PxbOJ52F37d2Y5Fws/AUkNnNEsan/WRJA1kuWoS6rpeR8JQYuVhLiK2u/KpOcvMVRw3Q2VUxtcAGw==" MetadataSize="58315" event="postinstall" sha256="DIAVxoI+8NpsudUawOA5U92VHlaxQBS3ejN4EPM6T2A="/>
+          <action ChromeOSVersion="3095.0.0" ChromeVersion="24.0.1307.0" IsDelta="true" IsDeltaPayload="false" MaxDaysToScatter="14" MetadataSignatureRsa="xXrO/LahHlKk3YmqEf1qE0PN587Sc2IJV+FN7J7x1h49waNQIy/QwYO4LaOySgETe5JZXtkAEzzqakfJwxQ2pVfzj1GkExwjd5LTn1He2GvA73B8fKbS4bfP7dbUFwD5039xCwf1U2gezFViOiOPiVURx/pEsdhv+Cqx/3HbjIuj5au2dooSyDxLC5AnODzAKyYfAcjMuiLON+9SqmctJW+VjzdY9SbJAnkH2qqVjFyBKAXsYT+hOTIJ3MJpg8OSVxMMtGB99PxbOJ52F37d2Y5Fws/AUkNnNEsan/WRJA1kuWoS6rpeR8JQYuVhLiK2u/KpOcvMVRw3Q2VUxtcAGw==" MetadataSize="58315" event="postinstall" sha256="DIAVxoI+8NpsudUawOA5U92VHlaxQBS3ejN4EPM6T2A="/>
         </actions>
       </manifest>
     </updatecheck>