Add fallback for DocumentModeAssassin

chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java

Index: chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java
diff --git a/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java b/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java
index ed58e9da1c430e4c10eb786457dea0b222396752..ef8fbfe125cd92ecb701596d19b419ba4f755682 100644
--- a/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java
+++ b/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/tabmodel/document/MockActivityDelegate.java
@@ -69,6 +69,12 @@ public class MockActivityDelegate extends ActivityDelegate {
         }
     }
 
+    @Override
+    public void finishAllDocumentActivities() {
+        mRegularTasks.clear();
+        mIncognitoTasks.clear();
+    }
+
     /**
      * Adds a task to the recents list.
      * @param isIncognito Whether the task is an incognito task.