Bug 1543790 - Fix RDD sandboxing conditions so the parent and child processes agree. r=gcp

If the system doesn't support seccomp-bpf, the parent process won't
try to set up sandboxing, but the child process has a separate check that
didn't test for this, and ends up failing a release assertion (in
SandboxReporterClient, but we also release-assert that installing the
seccomp-bpf policy succeeds).

This patch just fixes the child-side conditional to match the intended
behavior, but in the long term we should consider redesigning SandboxInfo
to avoid this.

Differential Revision: https://phabricator.services.mozilla.com/D27624

--HG--
extra : moz-landing-system : lando

security/sandbox/linux/Sandbox.cpp

@@ -652,7 +652,8 @@ void SetMediaPluginSandbox(const char* aFilePath) {
 }
 
 void SetRemoteDataDecoderSandbox(int aBroker) {
-  if (PR_GetEnv("MOZ_DISABLE_RDD_SANDBOX") != nullptr) {
+  if (!SandboxInfo::Get().Test(SandboxInfo::kHasSeccompBPF) ||
+      PR_GetEnv("MOZ_DISABLE_RDD_SANDBOX")) {
     if (aBroker >= 0) {
       close(aBroker);
     }