chromium: add ability to control which sandbox is used

First step towards addressing #17460

In order to be able to run the SUID sandbox, which is good for security
and required to run Chromium with any kind of reasonable sandboxing when
using grsecurity kernels, we want to be able to control where the
sandbox comes from in the Chromium wrapper. This commit patches the
appropriate bit of source and adds the same old sandbox to the wrapper
(so it should be a no-op)

pkgs/applications/networking/browsers/chromium/common.nix

···
     ];
 
     postPatch = ''
+      # We want to be able to specify where the sandbox is via CHROME_DEVEL_SANDBOX
+      substituteInPlace sandbox/linux/suid/client/setuid_sandbox_host.cc \
+        --replace \
+          'std::string sandbox_binary(GetSandboxBinaryPath().value());' \
+          'std::string sandbox_binary(GetDevelSandboxPath());'
+
       sed -i -r \
         -e 's/-f(stack-protector)(-all)?/-fno-\1/' \
         -e 's|/bin/echo|echo|' \

pkgs/applications/networking/browsers/chromium/default.nix

···
 
     ln -s "${chromium.browser}/share" "$out/share"
     eval makeWrapper "${browserBinary}" "$out/bin/chromium" \
+      --set CHROME_DEVEL_SANDBOX "${chromium.browser}/libexec/chromium/chrome-sandbox" \
       ${concatMapStringsSep " " getWrapperFlags chromium.plugins.enabled}
 
     ln -s "$out/bin/chromium" "$out/bin/chromium-browser"