[Memory-UMA] Implement basic working prototype.

base/trace_event/memory_allocator_dump.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 "base/trace_event/memory_allocator_dump.h"
 
 #include "base/format_macros.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/memory_dump_provider.h"
@@ skipping 68 matching lines @@
   attributes_->SetDouble("value", value);
   attributes_->EndDictionary();
 }
 
 void MemoryAllocatorDump::AddString(const char* name,
                                     const char* units,
                                     const std::string& value) {
   // String attributes are disabled in background mode.
   if (process_memory_dump_->dump_args().level_of_detail ==
       MemoryDumpLevelOfDetail::BACKGROUND) {
-    NOTREACHED();

[Primiano Tucci (use gerrit), 2017/05/15 03:48:09]

Hmm why? This shouldn't really happen. If it happens some MDP is broken.
if they are doing an AddString into BACKGROUND mode they will be likely doing
some non-cheap traversal of their structs

[erikchen, 2017/05/15 17:29:15]

Done.

     return;
   }
 
   attributes_->BeginDictionary(name);
   attributes_->SetString("type", kTypeString);
   attributes_->SetString("units", units);
   attributes_->SetString("value", value);
   attributes_->EndDictionary();
 }
 
 void MemoryAllocatorDump::AsValueInto(TracedValue* value) const {
   value->BeginDictionaryWithCopiedName(absolute_name_);
   value->SetString("guid", guid_.ToString());
   value->SetValue("attrs", *attributes_);
   if (flags_)
     value->SetInteger("flags", flags_);
   value->EndDictionary();  // "allocator_name/heap_subheap": { ... }
 }
 
 }  // namespace trace_event
 }  // namespace base