hiddenapi: Turn CHECK into a warning

We create a dummy hiddenapi-flags.csv file for ART buildbots but
Recent change to `hiddenapi` started enforcing that every dex member
has a corresponding CSV entry. Turn the CHECK into a LOG(WARNING) for
the time being to unblock the bots.

Test: rely on the ART Buildbot
Change-Id: I02565a0f11039dc28d395872d99adc7067d7e426
diff --git a/tools/hiddenapi/hiddenapi.cc b/tools/hiddenapi/hiddenapi.cc
index decbc01..0c6228b 100644
--- a/tools/hiddenapi/hiddenapi.cc
+++ b/tools/hiddenapi/hiddenapi.cc
@@ -952,8 +952,11 @@
           auto fn_shared = [&](const DexMember& boot_member) {
             auto it = api_list.find(boot_member.GetApiEntry());
             bool api_list_found = (it != api_list.end());
-            CHECK(!force_assign_all_ || api_list_found)
-                << "Could not find flags for dex entry: " << boot_member.GetApiEntry();
+            // TODO: Fix ART buildbots and turn this into a CHECK.
+            if (force_assign_all && !api_list_found) {
+              LOG(WARNING) << "Could not find hiddenapi flags for dex entry: "
+                           << boot_member.GetApiEntry();
+            }
             builder.WriteFlags(api_list_found ? it->second : hiddenapi::ApiList::Whitelist());
           };
           auto fn_field = [&](const ClassAccessor::Field& boot_field) {