[memory-infra] Log reasons for memory dump failure

components/tracing/child/child_memory_dump_manager_delegate_impl.cc

 // Copyright 2015 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 "components/tracing/child/child_memory_dump_manager_delegate_impl.h"
 
 #include "base/single_thread_task_runner.h"
 #include "build/build_config.h"
 #include "components/tracing/child/child_trace_message_filter.h"
 #include "components/tracing/common/process_metrics_memory_dump_provider.h"
@@ skipping 57 matching lines @@
   // RequestGlobalMemoryDump can be called on any thread, cannot access
   // ctmf_task_runner_ as it could be racy.
   scoped_refptr<base::SingleThreadTaskRunner> ctmf_task_runner;
   {
     base::AutoLock lock(lock_);
     ctmf_task_runner = ctmf_task_runner_;
   }
 
   // Bail out if we receive a dump request from the manager before the
   // ChildTraceMessageFilter has been initialized.
-  if (!ctmf_task_runner)
+  if (!ctmf_task_runner) {
+    VLOG(1) << base::trace_event::MemoryDumpManager::kLogPrefix
+            << " failed because child trace message filter hasn't been"
+            << " initialized";
     return AbortDumpRequest(args, callback);
+  }
 
   // Make sure we access |ctmf_| only on the thread where it lives to avoid
   // races on shutdown.
   if (!ctmf_task_runner->BelongsToCurrentThread()) {
     const bool did_post_task = ctmf_task_runner->PostTask(
         FROM_HERE,
         base::Bind(&ChildMemoryDumpManagerDelegateImpl::RequestGlobalMemoryDump,
                    base::Unretained(this), args, callback));
     if (!did_post_task)
       return AbortDumpRequest(args, callback);
     return;
   }
 
   // The ChildTraceMessageFilter could have been destroyed while hopping on the
   // right thread. If this is the case, bail out.
-  if (!ctmf_)
+  if (!ctmf_) {
+    VLOG(1) << base::trace_event::MemoryDumpManager::kLogPrefix
+            << " failed because child trace message filter was"
+            << " destroyed while switching threads";
     return AbortDumpRequest(args, callback);
+  }
 
   // Send the request up to the browser process' MessageDumpmanager.
   ctmf_->SendGlobalMemoryDumpRequest(args, callback);
 }
 
 uint64_t ChildMemoryDumpManagerDelegateImpl::GetTracingProcessId() const {
   return tracing_process_id_;
 }
 
 }  // namespace tracing