Show AlertDialog when WebAPKs are enabled in chrome://flags but Unknown sources is disabled

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
index ec5babba7b5de48610d59f741e70b5adc6d69d4e..a25c87047c2f67b413ad634803df45bb890c8a84 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
@@ -99,6 +99,7 @@ import org.chromium.chrome.browser.toolbar.ToolbarControlContainer;
 import org.chromium.chrome.browser.util.FeatureUtilities;
 import org.chromium.chrome.browser.util.IntentUtils;
 import org.chromium.chrome.browser.vr_shell.VrShellDelegate;
+import org.chromium.chrome.browser.webapps.ChromeWebApkHost;
 import org.chromium.chrome.browser.widget.emptybackground.EmptyBackgroundViewWrapper;
 import org.chromium.chrome.browser.widget.findinpage.FindToolbarManager;
 import org.chromium.content.browser.ContentVideoView;
@@ -382,6 +383,10 @@ public class ChromeTabbedActivity extends ChromeActivity implements OverviewMode
                 } else {
                     preferenceManager.setPromosSkippedOnFirstStart(true);
                 }
+
+                // Notify users experimenting with WebAPKs if they need to do extra steps to enable
+                // WebAPKs.
+                ChromeWebApkHost.launchWebApkRequirementsDialogIfNeeded(this);
             }
 
             initializeUI();