Fall back to shortcut A2HS when Phonesky is out of date or unavailable.

chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java
index 5bcfc29be1eda30ca1c86f1e8a9deb4b03adda78..98d86da299b9a5274c88f4d683fe123a0578bbb0 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java
@@ -51,4 +51,11 @@ public interface GooglePlayWebApkInstallDelegate {
      * @param event The result of the install.
      */
     void onGotInstallEvent(String packageName, @InstallerPackageEvent int event);
+
+    /**
+     * Checks whether Google Play Install API is available.
+     * @param callback The callback to invoke when the check is done.
+     * @return True if the Install API is available.

[dominickn, 2017/02/06 05:22:49]

I would make this method return void. It will only return false if there's no
need to do an async check, but you still call the callback anyway and ignore the
return value.

[Xi Han, 2017/02/06 18:03:43]

Done.

+     */
+    boolean canUseInstallApi(Callback<Boolean> callback);

[dominickn, 2017/02/06 05:22:49]

Just call this canInstallWebApk()?

[Xi Han, 2017/02/06 18:03:43]

Done.

 }