We've implemented these checks by: 
1) chrome check whether the webapk is a valid webapk
2) webapk checking caller is chrome

This bug is not WontFix. Our use of WebApkUtils#isValidWebApk() and WebApkUtils#queryWebApkPackage() is inconsistent. When is WebApkUtils#isValidWebApk() sufficient and when are both WebApkUtils#isValidWebApk() and WebApkUtils#queryWebApkPackage() required? I have https://codereview.chromium.org/2109033002/ up for review to address this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/82d265d97abff26f8ed3e432c63ee2fcfd456e99

commit 82d265d97abff26f8ed3e432c63ee2fcfd456e99
Author: pkotwicz <pkotwicz@chromium.org>
Date: Tue Jul 05 19:38:44 2016

Cleanup usage of WebApkValidator in notification code

This CL:
- Makes calls to WebApkValidator#queryWebApkPackage() and
  WebApkValidator#findWebApkPackage() call WebApkValidator#isValidWebApk().
- Removes WebApkValidator#queryWebApkPackage() call from
  NotificationPlatformBridge#dispatchNotificationEvent(). The check is
  unnecessary because
  org.chromium.chrome.browser.notifications.NotificationService is not
  exported.

BUG= 613024 

Review-Url: https://codereview.chromium.org/2109033002
Cr-Commit-Position: refs/heads/master@{#403816}

[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegate.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationHandler.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationPlatformBridge.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappLauncherActivity.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/javatests/src/org/chromium/chrome/browser/externalnav/ExternalNavigationHandlerTest.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/webapk/libs/client/junit/src/org/chromium/webapk/lib/client/WebApkValidatorTest.java
[modify] https://crrev.com/82d265d97abff26f8ed3e432c63ee2fcfd456e99/chrome/android/webapk/libs/client/src/org/chromium/webapk/lib/client/WebApkValidator.java