Update FlatBuffers to include multiple improvements.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 205 matching lines @@
   'src/third_party/yasm/source/patched-yasm':
     Var('chromium_git') + '/chromium/deps/yasm/patched-yasm.git' + '@' + '7da28c6c7c6a1387217352ce02b31754deb54d2a',
 
   'src/third_party/libjpeg_turbo':
     Var('chromium_git') + '/chromium/deps/libjpeg_turbo.git' + '@' + 'a1750dbc79a8792dde3d3f7d7d8ac28ba01ac9dd',
 
   'src/third_party/flac':
     Var('chromium_git') + '/chromium/deps/flac.git' + '@' + '7d0f5b3a173ffe98db08057d1f52b7787569e0a6',
 
   'src/third_party/flatbuffers/src':
-    Var('chromium_git') + '/external/github.com/google/flatbuffers.git' + '@' + 'e92ae5199d52fd59540a800bec7eef46cd778257',
+    Var('chromium_git') + '/external/github.com/google/flatbuffers.git' + '@' + 'c559eb451e7783b72c44e27db375158edaa498b7',
 
   'src/third_party/pyftpdlib/src':
     Var('chromium_git') + '/external/pyftpdlib.git' + '@' + '2be6d65e31c7ee6320d059f581f05ae8d89d7e45',
 
   'src/third_party/scons-2.0.1':
     Var('chromium_git') + '/native_client/src/third_party/scons-2.0.1.git' + '@' + '1c1550e17fc26355d08627fbdec13d8291227067',
 
   'src/third_party/webrtc':
     Var('chromium_git') + '/external/webrtc/trunk/webrtc.git' + '@' + '9d4241cbf21ab48686b80918bf5e4d72f2c15574', # commit position 18140
 
@@ skipping 919 matching lines @@
 recursedeps = [
   # buildtools provides clang_format, libc++, and libc++abi
   'src/buildtools',
   # android_tools manages the NDK.
   'src/third_party/android_tools',
   # ANGLE manages DEPS that it also owns the build files for, such as dEQP.
   ("src/third_party/angle", "DEPS.chromium"),
   # SwiftShader manages DEPS that it also owns the build files for, such as Subzero.
   ("src/third_party/swiftshader", "DEPS"),
 ]