For my checkout on a GNU/Linux machine, I have the following .gclient file:

===================
solutions = [
  { 
    "managed": False,
    "name": "src",
    "url": "https://chromium.googlesource.com/chromium/src.git",
    "custom_deps": {
      "src/third_party/adobe/flash/binaries/ppapi/linux": None,
      "src/third_party/adobe/flash/binaries/ppapi/linux_x64": None,
      "src/third_party/adobe/flash/symbols/ppapi/linux": None,
      "src/third_party/adobe/flash/symbols/ppapi/linux_x64": None,
    },
    "deps_file": ".DEPS.git",
    "safesync_url": "",
  },
  { "name"        : "src-internal",
     "url"          : <URL redacted>,
     "deps_file"    : ".DEPS.git",
  },
]
===================

When I do gclient sync, I see:

[0:08:01] Still working on:
[0:08:01]   src/third_party/adobe/flash/symbols/ppapi/linux
[0:08:01]   src/third_party/adobe/flash/symbols/ppapi/linux_x64


Expected:
The "None" value in .gclient should have prevented fetching the ppapi symbols.

Actual:
All 9+GB of the symbols seem to be downloaded.