Remove mActivity from Tab and look at windowAndroid for tab

chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java b/chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java
index 9b1091bfadc9bfeda1519147174a6e8fc3013f7a..76be018f683cd03b6450c463857d582ceb7ab4bc 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tab/ChromeTab.java
@@ -102,9 +102,9 @@ public class ChromeTab extends Tab {
 
         addObserver(mTabObserver);
 
-        if (mActivity != null && creationState != null) {
+        if (getTabModelSelector() != null && creationState != null) {
             setTabUma(new TabUma(
-                    this, creationState, mActivity.getTabModelSelector().getModel(incognito)));
+                    this, creationState, getTabModelSelector().getModel(incognito)));
         }
 
         if (incognito) {
@@ -462,7 +462,8 @@ public class ChromeTab extends Tab {
      * @return A new instance of {@link InterceptNavigationDelegateImpl}.
      */
     protected InterceptNavigationDelegateImpl createInterceptNavigationDelegate() {
-        return new InterceptNavigationDelegateImpl(mActivity, this);
+        assert getActivity() != null;
+        return new InterceptNavigationDelegateImpl(getActivity(), this);
     }
 
     /**
@@ -473,7 +474,7 @@ public class ChromeTab extends Tab {
     }
 
     public ReaderModeActivityDelegate getReaderModeActivityDelegate() {
-        return mActivity == null ? null : mActivity.getReaderModeActivityDelegate();
+        return getActivity() == null ? null : getActivity().getReaderModeActivityDelegate();
     }
 
     /**
@@ -483,9 +484,10 @@ public class ChromeTab extends Tab {
      * @return True, if a native page was displayed for url.
      */
     private boolean maybeShowNativePage(String url, boolean isReload) {
+        if (getTabModelSelector() == null) return false;
         NativePage candidateForReuse = isReload ? null : getNativePage();
         NativePage nativePage = NativePageFactory.createNativePageForURL(url, candidateForReuse,
-                this, mActivity.getTabModelSelector(), mActivity);
+                this, getTabModelSelector(), getActivity());
         if (nativePage != null) {
             showNativePage(nativePage);
             notifyPageTitleChanged();