[Android] Suppress javascript dialogs from background tabs in custom tab

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java
index 690cc6c80ebd13f47793b4166dfe400f85d1a1b3..bdfab22c39b9d4a235423220aab03c9773c5c6c5 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabDelegateFactory.java
@@ -24,6 +24,7 @@ import org.chromium.chrome.browser.tab.TabDelegateFactory;
 import org.chromium.chrome.browser.tab.TabWebContentsDelegateAndroid;
 import org.chromium.chrome.browser.tab.TopControlsVisibilityDelegate;
 import org.chromium.chrome.browser.util.UrlUtilities;
+import org.chromium.content_public.browser.WebContents;
 
 /**
  * A {@link TabDelegateFactory} class to be used in all {@link Tab} owned
@@ -129,6 +130,12 @@ public class CustomTabDelegateFactory extends TabDelegateFactory {
         }
 
         @Override
+        public boolean shouldSuppressDialogs(WebContents webContents) {
+            // If a tab is in the background, it should not be able to pop up a dialog.
+            return mTab.isHidden();
+        }
+
+        @Override
         public boolean shouldResumeRequestsForCreatedWindow() {
             return true;
         }