Devtools/tracing: Propagate errors from the tracing service dying

Right now if the utility process hosting the tracing service crashes
while tracing is in progress, the error isn't propagated and the
Tracing.end request will just eventually time out. Instead we now
throw an error right away to make these crashes more actionable.

R=caseq@chromium.org

Bug: 956191
Change-Id: Ie0f176676e9dc5e4ce29b3c228df56180975d483
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603830
Commit-Queue: oysteine <oysteine@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658407}

content/browser/devtools/protocol/tracing_handler.cc

@@ -242,6 +242,7 @@ class TracingHandler::TracingSession {
       base::OnceCallback<void(float percent_full,
                               size_t approximate_event_count)>
           on_buffer_usage_callback) = 0;
+  virtual bool HasTracingFailed() = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TracingSession);
@@ -282,6 +283,8 @@ class TracingHandler::LegacyTracingSession
     TracingController::GetInstance()->GetTraceBufferUsage(
         std::move(on_buffer_usage_callback));
   }
+
+  bool HasTracingFailed() override { return false; }
 };
 
 class TracingHandler::PerfettoTracingSession
@@ -290,19 +293,16 @@ class TracingHandler::PerfettoTracingSession
       public mojo::DataPipeDrainer::Client {
  public:
   ~PerfettoTracingSession() override {
-#if DCHECK_IS_ON()
     DCHECK(!tracing_active_);
-#endif
   }
 
   // TracingHandler::TracingSession implementation:
   void EnableTracing(const base::trace_event::TraceConfig& chrome_config,
                      base::OnceClosure on_recording_enabled_callback) override {
     DCHECK(!tracing_session_host_);
-#if DCHECK_IS_ON()
     DCHECK(!tracing_active_);
     tracing_active_ = true;
-#endif
+
     ServiceManagerConnection::GetForProcess()->GetConnector()->BindInterface(
         tracing::mojom::kServiceName, &consumer_host_);
 
@@ -355,12 +355,12 @@ class TracingHandler::PerfettoTracingSession
     use_proto_format_ = use_proto_format;
     agent_label_ = agent_label;
     endpoint_ = endpoint;
-#if DCHECK_IS_ON()
     tracing_active_ = false;
-#endif
 
     if (!tracing_session_host_) {
-      OnTracingSessionFailed();
+      if (endpoint_)
+        endpoint_->ReceiveTraceFinalContents(nullptr);
+
       return;
     }
 
@@ -409,6 +409,10 @@ class TracingHandler::PerfettoTracingSession
     std::move(on_buffer_usage_callback).Run(percent_full, 0);
   }
 
+  bool HasTracingFailed() override {
+    return tracing_active_ && !tracing_session_host_;
+  }
+
   // tracing::mojom::TracingSessionClient implementation:
   void OnTracingEnabled() override {
     if (on_recording_enabled_callback_) {
@@ -471,6 +475,13 @@ class TracingHandler::PerfettoTracingSession
     tracing_session_host_.reset();
     binding_.Close();
     drainer_.reset();
+
+    if (on_recording_enabled_callback_)
+      std::move(on_recording_enabled_callback_).Run();
+
+    if (pending_disable_tracing_task_)
+      std::move(pending_disable_tracing_task_).Run();
+
     if (endpoint_) {
       // TODO(oysteine): Signal to the client that tracing failed.
       endpoint_->ReceiveTraceFinalContents(nullptr);
@@ -514,9 +525,9 @@ class TracingHandler::PerfettoTracingSession
   std::unique_ptr<mojo::DataPipeDrainer> drainer_;
   bool data_complete_ = false;
   bool read_buffers_complete_ = false;
+  bool tracing_active_ = false;
 
 #if DCHECK_IS_ON()
-  bool tracing_active_ = false;
   base::trace_event::TraceConfig last_config_for_perfetto_;
 #endif
 };
@@ -859,6 +870,9 @@ Response TracingHandler::End() {
   if (!session_)
     return Response::Error("Tracing is not started");
 
+  if (session_->HasTracingFailed())
+    return Response::Error("Tracing failed");
+
   scoped_refptr<TracingController::TraceDataEndpoint> endpoint;
   if (return_as_stream_) {
     endpoint = new DevToolsStreamEndpoint(