[DevTools] Rework DevToolsSession interaction with domain handlers.

content/browser/devtools/protocol/target_handler.cc

Index: content/browser/devtools/protocol/target_handler.cc
diff --git a/content/browser/devtools/protocol/target_handler.cc b/content/browser/devtools/protocol/target_handler.cc
index 78778f4bd06e36da6eb449c3842d9b133b13fd1e..c17b128289aa5d7ed743acbfb635842b61aba894 100644
--- a/content/browser/devtools/protocol/target_handler.cc
+++ b/content/browser/devtools/protocol/target_handler.cc
@@ -5,6 +5,7 @@
 #include "content/browser/devtools/protocol/target_handler.h"
 
 #include "content/browser/devtools/devtools_manager.h"
+#include "content/browser/devtools/devtools_session.h"
 #include "content/browser/devtools/service_worker_devtools_agent_host.h"
 #include "content/browser/frame_host/frame_tree.h"
 #include "content/browser/frame_host/frame_tree_node.h"
@@ -93,7 +94,8 @@ std::unique_ptr<Target::TargetInfo> CreateInfo(DevToolsAgentHost* host) {
 }  // namespace
 
 TargetHandler::TargetHandler()
-    : discover_(false),
+    : DevToolsDomainHandler(Target::Metainfo::domainName),
+      discover_(false),
       auto_attach_(false),
       wait_for_debugger_on_start_(false),
       attach_to_frames_(false),
@@ -103,6 +105,12 @@ TargetHandler::TargetHandler()
 TargetHandler::~TargetHandler() {
 }
 
+// static
+TargetHandler* TargetHandler::FromSession(DevToolsSession* session) {
+  return static_cast<TargetHandler*>(
+      session->GetHandlerByName(Target::Metainfo::domainName));
+}
+
 void TargetHandler::Wire(UberDispatcher* dispatcher) {
   frontend_.reset(new Target::Frontend(dispatcher->channel()));
   Target::Dispatcher::wire(dispatcher, this);