Fix broken PWA notification badge.

The WebApkServiceClient was overwriting the small icon in the
notification builder. This change checks whether there was already a
provided small icon bitmap before overwriting.

This is the CL that introduced the bug:
https://chromium-review.googlesource.com/c/chromium/src/+/978126
It will always call setSmallIconForRemoteApp on the notification builder for PWAs. For Android M+
this will overwrite the provided small icon bitmap.

Bug: 867351
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: If65970f3349e6a0738003d89e2721e3b2568afdc
Reviewed-on: https://chromium-review.googlesource.com/1181043
Reviewed-by: Peter Conn <peconn@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#584475}(cherry picked from commit dc21e3e8e11747e461d69ae48b9e2bdb51d65e48)
Reviewed-on: https://chromium-review.googlesource.com/1183362
Cr-Commit-Position: refs/branch-heads/3497@{#738}
Cr-Branched-From: 271eaf50594eb818c9295dc78d364aea18c82ea8-refs/heads/master@{#576753}
3 files changed