Use the upstream version of libwebp, v0.4.3.

gyp/libwebp_skia.gypi

Index: gyp/libwebp_skia.gypi
diff --git a/gyp/libwebp_skia.gypi b/gyp/libwebp_skia.gypi
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+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This allows us to build libwebp with a custom config.h file. It is currently
+# needed to work around skbug.com/4037, but perhaps we might have another need
+# for it in the future.
+{
+  'include_dirs': [
+    '../third_party/libwebp/webp',
+  ],
+  'defines': [
+    'HAVE_CONFIG_H',
+  ],
+}