Use kRenderClientId command line flag when starting a render process

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 8ea4bb12aade5984c278edfbd451a37fde8103f0..d0b75bc835606a78b9c944eb22f062fd6ca1d9cf 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1584,6 +1584,18 @@ 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) {