[Custom Tabs]Fix a bug that activateContents will pop up a blank chrome

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

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTab.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTab.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTab.java
index c577a34d27c3ef149f0c99d0cb327ca479023140..b40f9a4e465faae371ed8aad320d362e60182729 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTab.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTab.java
@@ -371,6 +371,11 @@ public class CustomTab extends ChromeTab {
                 mTargetUrl = null;
                 return false;
             }
+
+            @Override
+            protected void bringActivityToForeground() {
+                // No-op here. If client's task is in background Chrome is unable to foreground it.
+            }
         };
     }
 }