Add an about:flag to control WebApk enablement.

chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java

Index: chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java b/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
index 9c36b82094f04b20ec9f5def6e953c65c571a46f..3fb87f92bb2cd82a67991f899fe65ae5eb763799 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
@@ -43,6 +43,7 @@ import org.chromium.chrome.browser.precache.PrecacheLauncher;
 import org.chromium.chrome.browser.preferences.ChromePreferenceManager;
 import org.chromium.chrome.browser.preferences.privacy.PrivacyPreferencesManager;
 import org.chromium.chrome.browser.share.ShareHelper;
+import org.chromium.chrome.browser.webapps.ChromeWebApkHost;
 import org.chromium.chrome.browser.webapps.WebApkVersionManager;
 import org.chromium.content.browser.ChildProcessLauncher;
 
@@ -257,7 +258,7 @@ public class DeferredStartupHandler {
                     // Initialize whether or not precaching is enabled.
                     PrecacheLauncher.updatePrecachingEnabled(mAppContext);
 
-                    if (CommandLine.getInstance().hasSwitch(ChromeSwitches.ENABLE_WEBAPK)) {
+                    if (ChromeWebApkHost.isEnabled()) {
                         WebApkVersionManager.updateWebApksIfNeeded();
                     }