[DevTools] Rework DevToolsSession interaction with domain handlers.

content/browser/devtools/protocol/tracing_handler.cc

Index: content/browser/devtools/protocol/tracing_handler.cc
diff --git a/content/browser/devtools/protocol/tracing_handler.cc b/content/browser/devtools/protocol/tracing_handler.cc
index eb6f29cacbe8aaa93e24fc0854981db228200daf..4159af138cb4296beebee9a488d313d4889eb56d 100644
--- a/content/browser/devtools/protocol/tracing_handler.cc
+++ b/content/browser/devtools/protocol/tracing_handler.cc
@@ -19,6 +19,7 @@
 #include "base/trace_event/tracing_agent.h"
 #include "components/tracing/browser/trace_config_file.h"
 #include "content/browser/devtools/devtools_io_context.h"
+#include "content/browser/devtools/devtools_session.h"
 #include "content/browser/tracing/tracing_controller_impl.h"
 
 namespace content {
@@ -118,7 +119,8 @@ class DevToolsStreamEndpoint : public TraceDataEndpoint {
 TracingHandler::TracingHandler(TracingHandler::Target target,
                                int frame_tree_node_id,
                                DevToolsIOContext* io_context)
-    : target_(target),
+    : DevToolsDomainHandler(Tracing::Metainfo::domainName),
+      target_(target),
       io_context_(io_context),
       frame_tree_node_id_(frame_tree_node_id),
       did_initiate_recording_(false),
@@ -128,6 +130,12 @@ TracingHandler::TracingHandler(TracingHandler::Target target,
 TracingHandler::~TracingHandler() {
 }
 
+// static
+TracingHandler* TracingHandler::FromSession(DevToolsSession* session) {
+  return static_cast<TracingHandler*>(
+      session->GetHandlerByName(Tracing::Metainfo::domainName));
+}
+
 void TracingHandler::Wire(UberDispatcher* dispatcher) {
   frontend_.reset(new Tracing::Frontend(dispatcher->channel()));
   Tracing::Dispatcher::wire(dispatcher, this);