Reduce capture frequency

 Bug: 5142655
 Only capture while the navscreen is visible
 Fix Tab.capture to never capture the title bar
 Fix navscreen not responding to updated thumbnails

Change-Id: Id48ad32bb131c398c7d1ce4243e92f04cd421ade
diff --git a/src/com/android/browser/BrowserWebView.java b/src/com/android/browser/BrowserWebView.java
index 38bbf90..dd93c1f 100644
--- a/src/com/android/browser/BrowserWebView.java
+++ b/src/com/android/browser/BrowserWebView.java
@@ -17,6 +17,7 @@
 package com.android.browser;
 
 import android.content.Context;
+import android.graphics.Canvas;
 import android.util.AttributeSet;
 import android.view.View;
 import android.webkit.WebView;
@@ -99,4 +100,8 @@
         }
     }
 
+    public void drawContent(Canvas c) {
+        onDraw(c);
+    }
+
 }