Use kRenderClientId command line flag when starting a render process

content/renderer/render_thread_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_thread_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <utility>
@@ skipping 1566 matching lines @@
     audio_renderer_mixer_manager_ = AudioRendererMixerManager::Create();
   }
 
   return audio_renderer_mixer_manager_.get();
 }
 
 base::WaitableEvent* RenderThreadImpl::GetShutdownEvent() {
   return ChildProcess::current()->GetShutDownEvent();
 }
 
+int32_t RenderThreadImpl::GetClientId() {
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kRendererClientId)) {

[piman, 2016/10/31 20:34:09]

nit: When would this happen? Only tests? If so, can you document that it's the
case?

[Alex Z., 2016/11/07 19:37:43]

This happens when running in single-process mode for debugging purposes. I have
documented it.

+    return 1;
+  }
+  int client_id = 0;
+  base::StringToInt(base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+                        switches::kRendererClientId),
+                    &client_id);

[piman, 2016/10/31 20:34:09]

Parsing strings (twice) seems like a bit of a heavy cost for something that
looks cheap ("get client id"). Can we do this in the constructor?

[Alex Z., 2016/11/07 19:37:43]

Done.

+  return client_id;
+}
+
 void RenderThreadImpl::OnAssociatedInterfaceRequest(
     const std::string& name,
     mojo::ScopedInterfaceEndpointHandle handle) {
   associated_interfaces_.BindRequest(name, std::move(handle));
 }
 
 bool RenderThreadImpl::IsGpuRasterizationForced() {
   return is_gpu_rasterization_forced_;
 }
 
@@ skipping 885 matching lines @@
   }
 }
 
 void RenderThreadImpl::OnRendererInterfaceRequest(
     mojom::RendererAssociatedRequest request) {
   DCHECK(!renderer_binding_.is_bound());
   renderer_binding_.Bind(std::move(request));
 }
 
 }  // namespace content