[CCT-Reparenting] Remove tab observer when the tab is removed from model

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

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
index e36d67d0c69e11766cf95599b7ea2ef9fad00e07..387652f8c82bc3ed1b2bd71722c33f0f07976122 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
@@ -176,6 +176,12 @@ public class CustomTabActivity extends ChromeActivity {
             // Finish the activity after we intent out.
             if (getTabModelSelector().getCurrentModel().getCount() == 0) finishAndClose(false);
         }
+
+        @Override
+        public void tabRemoved(Tab tab) {
+            tab.removeObserver(mTabObserver);
+            PageLoadMetrics.removeObserver(mMetricsObserver);
+        }
     };
 
     /**