Fix TabManager for Chrome Shell so it supports swapping WebContents.

chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java

Index: chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java
diff --git a/chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java b/chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java
index 0032af4c04b743d2e88efc6c8d99d1168d262839..b48a5bd657f56e3aba6ad9d76ed7c1f3d7bddb5d 100644
--- a/chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java
+++ b/chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java
@@ -11,7 +11,10 @@ import android.view.ViewGroup;
 import android.widget.FrameLayout;
 import android.widget.LinearLayout;
 
+import org.chromium.chrome.browser.EmptyTabObserver;
+import org.chromium.chrome.browser.Tab;
 import org.chromium.content.browser.ContentVideoViewClient;
+import org.chromium.content.browser.ContentView;
 import org.chromium.content.browser.ContentViewClient;
 import org.chromium.content.browser.ContentViewRenderView;
 import org.chromium.ui.base.WindowAndroid;
@@ -33,6 +36,7 @@ public class TabManager extends LinearLayout {
     private ChromeShellTab mCurrentTab;
 
     private String mStartupUrl = DEFAULT_URL;
+    private ContentView mCurrentContentView;
 
     /**
      * @param context The Context the view is running in.
@@ -122,11 +126,24 @@ public class TabManager extends LinearLayout {
         }
 
         mCurrentTab = tab;
+        mCurrentContentView = tab.getContentView();
+
+        mCurrentTab.addObserver(new EmptyTabObserver() {
+            @Override
+            public void onContentChanged(Tab tab) {
+                mContentViewHolder.removeView(mCurrentContentView);
+                setupContent(tab);
+            }
+        });
 
         mToolbar.showTab(mCurrentTab);
-        mContentViewHolder.addView(mCurrentTab.getContentView());
-        mContentViewRenderView.setCurrentContentViewCore(mCurrentTab.getContentViewCore());
-        mCurrentTab.getContentView().requestFocus();
-        mCurrentTab.getContentViewCore().onShow();
+        setupContent(mCurrentTab);
+    }
+
+    private void setupContent(Tab tab) {
+        mContentViewHolder.addView(tab.getContentView());
+        mContentViewRenderView.setCurrentContentViewCore(tab.getContentViewCore());
+        tab.getContentView().requestFocus();
+        tab.getContentViewCore().onShow();
     }
 }