update_engine: Add PayloadState Exclusion Logic

|PayloadState| will exclude payloads based on specific update failures.
This is to prevent critical platform updates from being blocked by less
critical updates (e.g. DLCs). A layer of robustness is added in
protecting CrOS devices from falling off the update train.

Some important changes to mention:
 - Only during updates will update_engine exclude non-critical payloads
 - |OmahaRequestAction|, the current precursor |Action| to
 |OmahaResponseHandlerAction|, during a update will exclude
 faulty/excluded payloads prior to setting the |OmahaResponse| as an
 output object for suqsequent bonded |Action| to consume
 - When all payloads are excluded for an update, the |ErrorCode| will
 be indicated as |OmahaResponseInvalid| as this case is not a valid
 Omaha response update_engine should ever run into because non-critical
 updates must tag alongside a critical update

BUG=chromium:928805
TEST=FEATURES=test emerge-$B update_engine update_engine-client

Change-Id: I0551a228d0b84defb4d59966e8ed46a5d9278d60
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2190237
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
diff --git a/common/utils.h b/common/utils.h
index d949a3e..ee2dce0 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -313,6 +313,10 @@
                              uint16_t* high_version,
                              uint16_t* low_version);
 
+// Returns the string format of the hashed |str_to_convert| that can be used
+// with |Excluder| as the exclusion name.
+std::string GetExclusionName(const std::string& str_to_convert);
+
 }  // namespace utils
 
 // Utility class to close a file descriptor