Fix silly bugs around overscan flag detection.

ui/base/x/x11_util.cc

 // Copyright (c) 2012 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.
 
 // This file defines utility functions for X11 (Linux only). This code has been
 // ported from XCB since we can't use XCB on Ubuntu while its 32-bit support
 // remains woefully incomplete.
 
 #include "ui/base/x/x11_util.h"
 
@@ skipping 1425 matching lines @@
       // - byte 1 high 3 bits: tag. '07' for extended tags.
       // - byte 1 remaining bits: the length of data block.
       // - byte 2: the extended tag.  '0' for video capability.
       // - byte 3: the capability.
       unsigned char tag = data_block[0] >> 5;
       unsigned char payload_length = data_block[0] & 0x1f;
       if (static_cast<unsigned long>(data_block + payload_length - prop) >
           nitems)
         break;
 
-      if (tag != kExtendedTag && payload_length < 2) {
+      if (tag != kExtendedTag || payload_length < 2) {
         data_block += payload_length + 1;
         continue;
       }
 
       unsigned char extended_tag_code = data_block[1];
       if (extended_tag_code != kExtendedVideoCapabilityTag) {
-        data_block += payload_length;
+        data_block += payload_length + 1;
         continue;
       }
 
       // The difference between preferred, IT, and CE video formats
       // doesn't matter. Sets |flag| to true if any of these flags are true.
       if ((data_block[2] & (1 << kPTOverscan)) ||
           (data_block[2] & (1 << kITOverscan)) ||
           (data_block[2] & (1 << kCEOverscan))) {
         *flag = true;
       } else {
@@ skipping 330 matching lines @@
       << "request_code " << static_cast<int>(error_event.request_code) << ", "
       << "minor_code " << static_cast<int>(error_event.minor_code)
       << " (" << request_str << ")";
 }
 
 // ----------------------------------------------------------------------------
 // End of x11_util_internal.h
 
 
 }  // namespace ui