Detach LeakDetectorController from remote controller on shutdown

chrome/browser/metrics/leak_detector/leak_detector_remote_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/metrics/leak_detector/leak_detector_remote_controller.h"
 
 #include "components/metrics/leak_detector/protobuf_to_mojo_converter.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace metrics {
@@ skipping 39 matching lines @@
     std::vector<mojom::MemoryLeakReportPtr> reports) {
   std::vector<MemoryLeakReportProto> report_protos;
   report_protos.reserve(reports.size());
 
   for (const mojom::MemoryLeakReportPtr& report : reports) {
     report_protos.push_back(MemoryLeakReportProto());
     MemoryLeakReportProto* proto = &report_protos.back();
 
     leak_detector::protobuf_to_mojo_converter::MojoToReport(*report, proto);
   }
-  DCHECK(g_local_controller);
-  g_local_controller->SendLeakReports(report_protos);
+  if (g_local_controller) {
+    g_local_controller->SendLeakReports(report_protos);
+  }
 }
 
 void LeakDetectorRemoteController::OnRemoteProcessShutdown() {
-  if (leak_detector_enabled_on_remote_process_) {
-    DCHECK(g_local_controller);
+  if (leak_detector_enabled_on_remote_process_ && g_local_controller) {
     g_local_controller->OnRemoteProcessShutdown();
   }
 }
 
 LeakDetectorRemoteController::LeakDetectorRemoteController(
     mojom::LeakDetectorRequest request)
     : binding_(this, std::move(request)),
       leak_detector_enabled_on_remote_process_(false) {
   binding_.set_connection_error_handler(
       base::Bind(&LeakDetectorRemoteController::OnRemoteProcessShutdown,
                  base::Unretained(this)));
 }
 
 // static
 void LeakDetectorRemoteController::SetLocalControllerInstance(
     LocalController* controller) {
+  // This must be on the same thread as the Mojo-based functions of this class,
+  // to avoid race conditions on |g_local_controller|.
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   g_local_controller = controller;
 }
 
 }  // namespace metrics