DevTools: speculative fix for crash in NetworkHandler::Disable

This keeps BrowserContext* and StoragePartition* instead of
RenderProcessHost* in an attemp to resolve UAF of RenderProcessHost
upon closure of DevTools front-end.

Bug: 801117, 783067, 780694
Change-Id: I6c2cca60cc0c29f0949d189cf918769059f80c1b
Reviewed-on: https://chromium-review.googlesource.com/876657
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531157}
SharedWorkerDevToolsAgentHost::SharedWorkerDevToolsAgentHost(
    SharedWorkerHost* worker_host,
    const base::UnguessableToken& devtools_worker_token)
    : DevToolsAgentHostImpl(devtools_worker_token.ToString()),
      state_(WORKER_NOT_READY),
      worker_host_(worker_host),
      devtools_worker_token_(devtools_worker_token),
      instance_(new SharedWorkerInstance(*worker_host->instance())) {
  NotifyCreated();
}

SharedWorkerDevToolsAgentHost::SharedWorkerDevToolsAgentHost(
    SharedWorkerHost* worker_host,
    const base::UnguessableToken& devtools_worker_token)
    : DevToolsAgentHostImpl(devtools_worker_token.ToString()),
      state_(WORKER_NOT_READY),
      worker_host_(worker_host),
      devtools_worker_token_(devtools_worker_token),
      instance_(new SharedWorkerInstance(*worker_host->instance())) {
  NotifyCreated();
}
