handle false results in file.delete and similar calls

found by findbugs
http://b/issue?id=1856614
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index 7b76cf8..6ea9ebb 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -279,7 +279,9 @@
         public Void doInBackground(File... files) {
             if (files != null) {
                 for (File f : files) {
-                    f.delete();
+                    if (!f.delete()) {
+                      Log.e(LOGTAG, f.getPath() + " was not deleted");
+                    }
                 }
             }
             return null;