remove save/restore picture from browser app

These pictures may be arbitrarily large, and with the
newer caching mechanism, are rarely used.

Also, remove any old pictures when the Browser starts.

Change-Id: I08e1720a198b159733fda819304dc6af6811390a
http://b/2650945
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index 1c32ecd..ad82fd0 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -368,6 +368,15 @@
             attachTabToContentView(mTabControl.getCurrentTab());
         }
 
+        // Delete old thumbnails to save space
+        File dir = mTabControl.getThumbnailDir();
+        if (dir.exists()) {
+            for (String child : dir.list()) {
+                File f = new File(dir, child);
+                f.delete();
+            }
+        }
+
         // Read JavaScript flags if it exists.
         String jsFlags = mSettings.getJsFlags();
         if (jsFlags.trim().length() != 0) {