Fall back to legacy add to homescreen behavior on non-GMS device or GMS isn't availabe.

chrome/browser/android/webapk/webapk_installer.h

Index: chrome/browser/android/webapk/webapk_installer.h
diff --git a/chrome/browser/android/webapk/webapk_installer.h b/chrome/browser/android/webapk/webapk_installer.h
index a987e0450a561c93aa2d51b67e14ee129fb45eaf..57eac566eea970d93cddb7d99631ca2ec9c2ba92 100644
--- a/chrome/browser/android/webapk/webapk_installer.h
+++ b/chrome/browser/android/webapk/webapk_installer.h
@@ -124,10 +124,11 @@ class WebApkInstaller : public net::URLFetcherDelegate {
       JNIEnv* env,
       const base::android::ScopedJavaLocalRef<jstring>& java_file_path);
 
-  // Returns whether the Google Play install delegate is available.
+  // Returns whether Google Play Service can be used and the install delegate is

[dominickn, 2017/01/18 00:07:02]

nit: "Google Play Services"

[Xi Han, 2017/01/18 14:53:27]

Done.

+  // available.
   // Note: it is possible that this delegate is null even when installing
   // WebAPKs using Google Play is enabled.
-  virtual bool HasGooglePlayWebApkInstallDelegate();
+  virtual bool CanUseGooglePlayInstallService();
 
   // Called when the package name of the WebAPK is available and the install
   // or update request is handled by Google Play.