Remove mActivity from Tab and look at windowAndroid for tab

chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java

Index: chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java b/chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java
index b28925371a0b2ebf2ecb4f2273b7215375770edb..2c0201a7d1420195cbb348d7a65f59142ee3cac4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/document/DocumentTab.java
@@ -46,8 +46,6 @@ public class DocumentTab extends ChromeTab {
     // Whether this document tab was constructed from passed-in web contents pointer.
     private boolean mCreatedFromWebContents;
 
-    private final DocumentActivity mActivity;
-
     /**
      * Standard constructor for the document tab.
      * @param activity The document activity that will hold on to this tab.
@@ -61,7 +59,6 @@ public class DocumentTab extends ChromeTab {
             String url, int parentTabId, boolean initiallyHidden) {
         super(ActivityDelegate.getTabIdFromIntent(activity.getIntent()), activity,
                 incognito, windowAndroid, TabLaunchType.FROM_EXTERNAL_APP, parentTabId, null, null);
-        mActivity = activity;
         initialize(url, null, activity.getTabContentManager(), false, initiallyHidden);
     }
 
@@ -78,7 +75,6 @@ public class DocumentTab extends ChromeTab {
             WindowAndroid windowAndroid, String url, TabState tabState, int parentTabId) {
         super(ActivityDelegate.getTabIdFromIntent(activity.getIntent()), activity,
                 incognito, windowAndroid, TabLaunchType.FROM_RESTORE, parentTabId, null, tabState);
-        mActivity = activity;
         initialize(url, null, activity.getTabContentManager(), true, false);
     }
 
@@ -96,7 +92,6 @@ public class DocumentTab extends ChromeTab {
         super(ActivityDelegate.getTabIdFromIntent(activity.getIntent()), activity,
                 incognito, windowAndroid, TabLaunchType.FROM_LONGPRESS_FOREGROUND,
                 parentTabId, null, null);
-        mActivity = activity;
         initialize(url, webContents, activity.getTabContentManager(), false, false);
         mCreatedFromWebContents = true;
     }
@@ -212,7 +207,7 @@ public class DocumentTab extends ChromeTab {
 
     @VisibleForTesting
     public DocumentActivity getActivity() {
-        return mActivity;
+        return getActivity();
     }
 
     /**
@@ -220,7 +215,6 @@ public class DocumentTab extends ChromeTab {
      * @param creationState In what state the tab was created.
      */
     public void initializeTabUma(TabCreationState creationState) {
-        setTabUma(new TabUma(this, creationState,
-                mActivity.getTabModelSelector().getModel(mActivity.isIncognito())));
+        setTabUma(new TabUma(this, creationState, getTabModelSelector().getModel(isIncognito())));
     }
 }