Thanks for filing the bug. I will take a look soon!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5b7fc7601292363b4b02869601b4b2c3010107c8

commit 5b7fc7601292363b4b02869601b4b2c3010107c8
Author: hanxi <hanxi@chromium.org>
Date: Wed Jun 28 18:17:37 2017

WebApk needs to be restarted to notice that host browser was uninstalled.

We cache a static variable for the WebAPK's runtime host, and it won't updated
when the runtime host is uninstalled. Therefore, the WebAPK won't launch until
it is forced to stop and relaunch. In this CL, we add an additional check of
whether the runtime host is installed. If not, continue the regular browser
selection process.

BUG= 736036 

Review-Url: https://codereview.chromium.org/2954933002
Cr-Commit-Position: refs/heads/master@{#483064}

[modify] https://crrev.com/5b7fc7601292363b4b02869601b4b2c3010107c8/chrome/android/webapk/shell_apk/junit/src/org/chromium/webapk/shell_apk/WebApkUtilsTest.java
[modify] https://crrev.com/5b7fc7601292363b4b02869601b4b2c3010107c8/chrome/android/webapk/shell_apk/shell_apk_version.gni
[modify] https://crrev.com/5b7fc7601292363b4b02869601b4b2c3010107c8/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/WebApkUtils.java