Add a mode flag to the tracing framework.

content/browser/tracing/tracing_ui.cc

Index: content/browser/tracing/tracing_ui.cc
diff --git a/content/browser/tracing/tracing_ui.cc b/content/browser/tracing/tracing_ui.cc
index 72f6451c429c3a5d08d1a8b78ba46f52e545435b..ecf129c21057a9ed65cbb9b3cfbb5d779a6766f8 100644
--- a/content/browser/tracing/tracing_ui.cc
+++ b/content/browser/tracing/tracing_ui.cc
@@ -372,7 +372,8 @@ void TracingMessageHandler::SaveTraceFileComplete() {
 
 void TracingMessageHandler::OnBeginTracing(const base::ListValue* args) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK_EQ(args->GetSize(), (size_t) 2);
+  DCHECK_GE(args->GetSize(), (size_t) 2);
+  DCHECK_LE(args->GetSize(), (size_t) 3);
 
   bool system_tracing_requested = false;
   bool ok = args->GetBoolean(0, &system_tracing_requested);
@@ -382,12 +383,20 @@ void TracingMessageHandler::OnBeginTracing(const base::ListValue* args) {
   ok = args->GetString(1, &chrome_categories);
   DCHECK(ok);
 
+  base::debug::TraceLog::TraceMode mode = base::debug::TraceLog::UNTIL_FULL;
+  if (args->GetSize() == 3) {

[nduca, 2013/02/21 05:40:16]

would be less fragile if you wrote >= 3

[dsinclair, 2013/02/21 16:26:04]

Done.

+    std::string mode_;
+    ok = args->GetString(2, &mode_);
+    DCHECK(ok);
+    mode = base::debug::TraceLog::TraceModeFromString(mode_);

[nduca, 2013/02/21 05:40:16]

might check with pavel, but i think you need to do the string-to-enum conversion
in devtools. Once released, the names we use on the devtool protocol handler we
have to commit to being backcompat. That's not the case for tracing_ui, and not
obvious when you're just a dude hacking in base/. That is to say, lets do this
per-instance conversion to enum here and in devtools, rather than sharing code.

[pfeldman, 2013/02/21 05:49:24]

Yep, you should have local conversion barrier in the devtools code.

[dsinclair, 2013/02/21 16:26:04]

Done.

[dsinclair, 2013/02/21 16:26:04]

Done.

I've made it a comma separated list, so devtools would receive
record-until-full,sampling and we'll split and turn into options from here.
(same with tracing_ui)

+  }
+
   trace_enabled_ = true;
   // TODO(jbates) This may fail, but that's OK for current use cases.
   //              Ex: Multiple about:gpu traces can not trace simultaneously.
   // TODO(nduca) send feedback to javascript about whether or not BeginTracing
   //             was successful.
-  TraceController::GetInstance()->BeginTracing(this, chrome_categories);
+  TraceController::GetInstance()->BeginTracing(this, chrome_categories, mode);
 
   if (system_tracing_requested) {
 #if defined(OS_CHROMEOS)