Add an about:flag to control WebApk enablement.

chrome/browser/android/shortcut_helper.cc

Index: chrome/browser/android/shortcut_helper.cc
diff --git a/chrome/browser/android/shortcut_helper.cc b/chrome/browser/android/shortcut_helper.cc
index 6ac62f1db48b442f74eb293007381e5a867f7637..c30ff516b35a0fde359c6d43e5967e9f94c937d4 100644
--- a/chrome/browser/android/shortcut_helper.cc
+++ b/chrome/browser/android/shortcut_helper.cc
@@ -72,8 +72,8 @@ void ShortcutHelper::AddToLauncherWithSkBitmap(
     const base::Closure& splash_image_callback) {
   if (info.display == blink::WebDisplayModeStandalone ||
       info.display == blink::WebDisplayModeFullscreen) {
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kEnableWebApk)) {
+    JNIEnv* env = base::android::AttachCurrentThread();
+    if (Java_ShortcutHelper_areWebApksEnabled(env)) {
       InstallWebApkWithSkBitmap(browser_context, info, icon_bitmap);
       return;
     }