DevTools Performance Timeline revisited (#1972)

The DevTools Performance Timeline is an implementation of a Trace
viewer.

On Chrome, the TracingController has several TracingAgents, each of
which outputs events in the Trace format.
These agents are mainly the Blink Trace agent, and a v8 js sampling
profiler, plus on Android, a java trace agent.

(https://github.com/youtube/cobalt/blob/f0d959a6920a8c481811c15ef4ebdbe8c6d0cc66/base/trace_event/tracing_agent.h#L21).
This CL should make it easier to add an Android tracing agent in the
future.

Previously, the Cobalt implementation did not have a TracingController,
and had a single agent which was plugged directly into the v8 profiler,
so we were blind to the rest of the callstack.

This CL introduces a TracingController with two agents, a
TraceEventsAgent, analogous to the Chrome Blink agent, which captures
the bulk of the data, and also a V8TracingAgent which is still plugged
into V8. I think the V8 agent still needs more work so even though its
implemented here, its currently disabled.

I also think we can lean into CDP (chrome devtools protocol) to get rid
of our custom CVal implmentation, which should get our Performance
testing closer to Chrome.


b/198688218
b/123369438

cobalt/debug/BUILD.gn

@@ -46,8 +46,8 @@ static_library("debug") {
     "backend/render_overlay.h",
     "backend/script_debugger_agent.cc",
     "backend/script_debugger_agent.h",
-    "backend/tracing_agent.cc",
-    "backend/tracing_agent.h",
+    "backend/tracing_controller.cc",
+    "backend/tracing_controller.h",
     "command.h",
     "console/debug_hub.cc",
     "console/debug_hub.h",

cobalt/debug/backend/debug_module.cc

@@ -30,7 +30,7 @@ constexpr char kDomAgent[] = "DomAgent";
 constexpr char kCssAgent[] = "CssAgent";
 constexpr char kOverlayAgent[] = "OverlayAgent";
 constexpr char kPageAgent[] = "PageAgent";
-constexpr char kTracingAgent[] = "TracingAgent";
+constexpr char kTracingController[] = "TracingController";
 
 // Move the state for a particular agent out of the dictionary holding the
 // state for all agents. Returns a NULL JSONObject if either |agents_state| is
@@ -161,8 +161,8 @@ void DebugModule::BuildInternal(const ConstructionData& data) {
                                     std::move(page_render_layer),
                                     data.resource_provider));
   }
-  tracing_agent_.reset(
-      new TracingAgent(debug_dispatcher_.get(), script_debugger_.get()));
+  tracing_controller_.reset(
+      new TracingController(debug_dispatcher_.get(), script_debugger_.get()));
 
   // Hook up hybrid agent JavaScript to the DebugBackend.
   debug_backend_->BindAgents(css_agent_);
@@ -190,7 +190,7 @@ void DebugModule::BuildInternal(const ConstructionData& data) {
     overlay_agent_->Thaw(RemoveAgentState(kOverlayAgent, agents_state));
   if (page_agent_)
     page_agent_->Thaw(RemoveAgentState(kPageAgent, agents_state));
-  tracing_agent_->Thaw(RemoveAgentState(kTracingAgent, agents_state));
+  tracing_controller_->Thaw(RemoveAgentState(kTracingController, agents_state));
 
   is_frozen_ = false;
 }
@@ -213,7 +213,8 @@ std::unique_ptr<DebuggerState> DebugModule::Freeze() {
     StoreAgentState(agents_state, kOverlayAgent, overlay_agent_->Freeze());
   if (page_agent_)
     StoreAgentState(agents_state, kPageAgent, page_agent_->Freeze());
-  StoreAgentState(agents_state, kTracingAgent, tracing_agent_->Freeze());
+  StoreAgentState(agents_state, kTracingController,
+                  tracing_controller_->Freeze());
 
   // Take the clients from the dispatcher last so they still get events that the
   // agents might send as part of being frozen.

cobalt/debug/backend/debug_module.h

@@ -33,7 +33,7 @@
 #include "cobalt/debug/backend/page_agent.h"
 #include "cobalt/debug/backend/render_overlay.h"
 #include "cobalt/debug/backend/script_debugger_agent.h"
-#include "cobalt/debug/backend/tracing_agent.h"
+#include "cobalt/debug/backend/tracing_controller.h"
 #include "cobalt/debug/json_object.h"
 #include "cobalt/dom/window.h"
 #include "cobalt/render_tree/resource_provider.h"
@@ -142,7 +142,7 @@ class DebugModule : public script::ScriptDebugger::Delegate {
   std::unique_ptr<OverlayAgent> overlay_agent_;
   std::unique_ptr<PageAgent> page_agent_;
   std::unique_ptr<ScriptDebuggerAgent> script_debugger_agent_;
-  std::unique_ptr<TracingAgent> tracing_agent_;
+  std::unique_ptr<TracingController> tracing_controller_;
 };
 
 }  // namespace backend