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

In tab reparenting, we never close but only remove the tab from the
model. During this process, both tab observer and also the metrics
observer was still kept, which leaked over some custom tab features into
the tab even after it was reparented. This removes the observers and
fixes the related issues.

TEST=CustomTabActivityTest#testTabReparentingBasic
BUG=669169

Review-Url: https://codereview.chromium.org/2539643002
Cr-Commit-Position: refs/heads/master@{#435028}

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);
+        }
     };
 
     /**

chrome/android/javatests/src/org/chromium/chrome/browser/customtabs/CustomTabActivityTest.java

@@ -41,6 +41,7 @@ import android.view.ViewGroup;
 import android.widget.EditText;
 import android.widget.ImageButton;
 
+import org.chromium.base.ObserverList.RewindableIterator;
 import org.chromium.base.PathUtils;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.library_loader.LibraryLoader;
@@ -65,6 +66,7 @@ import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tab.TabObserver;
+import org.chromium.chrome.browser.tab.TabTestUtils;
 import org.chromium.chrome.browser.tabmodel.EmptyTabModelObserver;
 import org.chromium.chrome.browser.tabmodel.TabModel.TabLaunchType;
 import org.chromium.chrome.browser.tabmodel.TabModelSelector;
@@ -1726,6 +1728,10 @@ public class CustomTabActivityTest extends CustomTabActivityTestBase {
         assertEquals("The tab should never be hidden during the reparenting process",
                 0, tabHiddenHelper.getCallCount());
         tabToBeReparented.removeObserver(observer);
+        RewindableIterator<TabObserver> observers = TabTestUtils.getTabObservers(tabToBeReparented);
+        while (observers.hasNext()) {
+            assertFalse(observers.next() instanceof CustomTabObserver);
+        }
         return newActivity;
     }