[tracing] Introduce BACKGROUND mode in MemoryInfra

base/trace_event/memory_dump_request_args.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_REQUEST_ARGS_H_
 #define BASE_TRACE_EVENT_MEMORY_DUMP_REQUEST_ARGS_H_
 
 // This file defines the types and structs used to issue memory dump requests.
 // These are also used in the IPCs for coordinating inter-process memory dumps.
 
@@ skipping 10 matching lines @@
 // selective enabling of dumps, filtering and post-processing.
 enum class MemoryDumpType {
   TASK_BEGIN,         // Dumping memory at the beginning of a message-loop task.
   TASK_END,           // Dumping memory at the ending of a message-loop task.
   PERIODIC_INTERVAL,  // Dumping memory at periodic intervals.
   EXPLICITLY_TRIGGERED,  // Non maskable dump request.
   LAST = EXPLICITLY_TRIGGERED // For IPC macros.
 };
 
 // Tells the MemoryDumpProvider(s) how much detailed their dumps should be.
-// MemoryDumpProvider instances must guarantee that level of detail does not
-// affect the total size reported in the root node, but only the granularity of
-// the child MemoryAllocatorDump(s).
 enum class MemoryDumpLevelOfDetail {
-  LIGHT,           // Few entries, typically a fixed number, per dump.
-  DETAILED,        // Unrestricted amount of entries per dump.
-  LAST = DETAILED  // For IPC Macros.
+  // For background tracing mode. The dump time is quick, and typically just the
+  // totals are expected. Suballocations need not be specified. Dump name must
+  // contain only pre-defined strings and string arguments cannot be added.
+  BACKGROUND,
+
+  // For the levels below, MemoryDumpProvider instances must guarantee that the
+  // total size reported in the root node is consistent. Only the granularity of
+  // the child MemoryAllocatorDump(s) differs with the levels.
+
+  // Few entries, typically a fixed number, per dump.
+  LIGHT,
+
+  // Unrestricted amount of entries per dump.
+  DETAILED,
+
+  // For IPC Macros.
+  LAST = DETAILED
 };
 
 // Initial request arguments for a global memory dump. (see
 // MemoryDumpManager::RequestGlobalMemoryDump()).
 struct BASE_EXPORT MemoryDumpRequestArgs {
   // Globally unique identifier. In multi-process dumps, all processes issue a
   // local dump with the same guid. This allows the trace importers to
   // reconstruct the global dump.
   uint64_t dump_guid;
 
   MemoryDumpType dump_type;
   MemoryDumpLevelOfDetail level_of_detail;
 };
 
 using MemoryDumpCallback = Callback<void(uint64_t dump_guid, bool success)>;
 
 BASE_EXPORT const char* MemoryDumpTypeToString(const MemoryDumpType& dump_type);
 
 BASE_EXPORT const char* MemoryDumpLevelOfDetailToString(
     const MemoryDumpLevelOfDetail& level_of_detail);
 
 BASE_EXPORT MemoryDumpLevelOfDetail
 StringToMemoryDumpLevelOfDetail(const std::string& str);
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_DUMP_REQUEST_ARGS_H_