Fix bug in one conditional. Add more apk test files.

chrome/android/webapk/libs/client/src/org/chromium/webapk/lib/client/WebApkVerifySignature.java

 // Copyright 2017 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.webapk.lib.client;
 
 import static java.nio.ByteOrder.LITTLE_ENDIAN;
 
 import android.support.annotation.IntDef;
 import android.util.Log;
@@ skipping 361 matching lines @@
         }
         if (!hasBlockAtStart) {
             return ERROR_BAD_BLANK_SPACE;
         }
         if (positionOfLastByteOfLastBlock != mCentralDirOffset) {
             seek(mCentralDirOffset - V2_SIGNING_MAGIC.length());
             String magic = readString(V2_SIGNING_MAGIC.length());
             if (V2_SIGNING_MAGIC.equals(magic)) {
                 // Only if we have a v2 signature do we allow medium sized gap between the last
                 // block and the start of the central directory.
-                if (positionOfLastByteOfLastBlock + MAX_V2_SIGNING_BLOCK_SIZE > mCentralDirOffset) {
+                if (mCentralDirOffset - positionOfLastByteOfLastBlock > MAX_V2_SIGNING_BLOCK_SIZE) {
                     return ERROR_BAD_V2_BLOCK;

[Xi Han, 2017/05/24 18:28:52]

Can you make this error more meaningful?

[ScottK, 2017/05/25 00:26:25]

Done.

                 }
             } else {
                 return ERROR_BAD_BLANK_SPACE;
             }
         }
         return ERROR_OK;
     }
 
     /**
      * We search buffer for EOCD_SIG and return the location where we found it. If the file has no
@@ skipping 67 matching lines @@
             return null;
         }
         byte[] data = new byte[len / 2];
         for (int i = 0; i < len; i += 2) {
             data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                     + Character.digit(s.charAt(i + 1), 16));
         }
         return data;
     }
 }