libwebp: update to 0.4.2-rc2

third_party/libwebp/libwebp.gyp

 # 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.
 
 {
   'variables': {
     'neon_sources': [
       'dsp/dec_neon.c',
       'dsp/enc_neon.c',
       'dsp/lossless_neon.c',
@@ skipping 30 matching lines @@
       'sources': [
         'demux/demux.c',
       ],
     },
     {
       'target_name': 'libwebp_dsp',
       'type': 'static_library',
       'include_dirs': ['.'],
       'sources': [
         'dsp/alpha_processing.c',
+        'dsp/alpha_processing_sse2.c',
         'dsp/cpu.c',
         'dsp/dec.c',
         'dsp/dec_clip_tables.c',
         'dsp/dec_mips32.c',
         'dsp/dec_sse2.c',
         'dsp/enc.c',
         'dsp/enc_avx2.c',
         'dsp/enc_mips32.c',
         'dsp/enc_sse2.c',
         'dsp/lossless.c',
@@ skipping 113 matching lines @@
       ],
       'direct_dependent_settings': {
         'include_dirs': ['.'],
       },
       'conditions': [
         ['OS!="win"', {'product_name': 'webp'}],
       ],
     },
   ],
 }