[memory-infra] Log reasons for memory dump failure

base/trace_event/memory_dump_manager.h

 // 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.
 
 #ifndef BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_
 #define BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 22 matching lines @@
 class MemoryDumpManagerDelegate;
 class MemoryDumpProvider;
 class MemoryDumpSessionState;
 
 // This is the interface exposed to the rest of the codebase to deal with
 // memory tracing. The main entry point for clients is represented by
 // RequestDumpPoint(). The extension by Un(RegisterDumpProvider).
 class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
  public:
   static const char* const kTraceCategory;
+  static const char* const kLogPrefix;
 
   // This value is returned as the tracing id of the child processes by
   // GetTracingProcessId() when tracing is not enabled.
   static const uint64_t kInvalidTracingProcessId;
 
   static MemoryDumpManager* GetInstance();
 
   // Invoked once per process to listen to trace begin / end events.
   // Initialization can happen after (Un)RegisterMemoryDumpProvider() calls
   // and the MemoryDumpManager guarantees to support this.
@@ skipping 343 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MemoryDumpManagerDelegate);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_