Use kRenderClientId command line flag when starting a render process

content/public/test/mock_render_thread.cc

Index: content/public/test/mock_render_thread.cc
diff --git a/content/public/test/mock_render_thread.cc b/content/public/test/mock_render_thread.cc
index e5edbf98e0518c35ae3a68e8ac2def16fc14863e..061b28c5f6aa4a4daed69db932e399a3f24fdad6 100644
--- a/content/public/test/mock_render_thread.cc
+++ b/content/public/test/mock_render_thread.cc
@@ -219,6 +219,10 @@ base::WaitableEvent* MockRenderThread::GetShutdownEvent() {
   return NULL;
 }
 
+int32_t MockRenderThread::GetClientId() {
+  return 1;
+}
+
 #if defined(OS_WIN)
 void MockRenderThread::PreCacheFont(const LOGFONT& log_font) {
 }