[Android] Fix findbugs errors.

media/base/android/java/src/org/chromium/media/MediaDrmBridge.java

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.media;
 
 import android.media.MediaCrypto;
 import android.media.MediaDrm;
 import android.os.AsyncTask;
 import android.os.Build;
@@ skipping 187 matching lines @@
             Log.e(TAG, "Cannot create MediaCrypto Session.");
             return false;
         }
         Log.d(TAG, "MediaCrypto Session created: " + mMediaCryptoSession);
 
         // Create MediaCrypto object.
         try {
             if (MediaCrypto.isCryptoSchemeSupported(mSchemeUUID)) {
                 final byte[] mediaCryptoSession = mMediaCryptoSession.array();
                 mMediaCrypto = new MediaCrypto(mSchemeUUID, mediaCryptoSession);
-                assert mMediaCrypto != null;
                 Log.d(TAG, "MediaCrypto successfully created!");
                 mSessionIds.put(mMediaCryptoSession, INVALID_SESSION_ID);
                 // Notify the native code that MediaCrypto is ready.
                 nativeOnMediaCryptoReady(mNativeMediaDrmBridge);
                 return true;
             } else {
                 Log.e(TAG, "Cannot create MediaCrypto for unsupported scheme.");
             }
         } catch (android.media.MediaCryptoException e) {
             Log.e(TAG, "Cannot create MediaCrypto", e);
@@ skipping 688 matching lines @@
 
     private native void nativeOnSessionClosed(long nativeMediaDrmBridge, int sessionId);
 
     private native void nativeOnSessionError(long nativeMediaDrmBridge, int sessionId);
 
     private native void nativeOnResetDeviceCredentialsCompleted(
             long nativeMediaDrmBridge, boolean success);
 
     private static native void nativeAddKeySystemUuidMapping(String keySystem, ByteBuffer uuid);
 }