[Startup Tracing] Add --trace-config-file flag

components/tracing/tracing_switches.cc

Index: components/tracing/tracing_switches.cc
diff --git a/components/tracing/tracing_switches.cc b/components/tracing/tracing_switches.cc
index fcec5eeed737598e47c0ac831c45edd0fda39312..711a5e4ca262d891579b86e5c40d524f12c7f047 100644
--- a/components/tracing/tracing_switches.cc
+++ b/components/tracing/tracing_switches.cc
@@ -6,6 +6,10 @@
 
 namespace switches {
 
+// Causes TRACE_EVENT flags to be recorded from startup.
+// This flag will be ignored if --trace-startup or --trace-shutdown is provided.
+const char kTraceConfigFile[]        = "trace-config-file";

[msw, 2015/08/25 18:06:49]

nit: match the spacing of other lines.

[Zhen Wang, 2015/08/25 18:18:37]

Done.

+
 // Causes TRACE_EVENT flags to be recorded beginning with shutdown. Optionally,
 // can specify the specific trace categories to include (e.g.
 // --trace-shutdown=base,net) otherwise, all events are recorded.