[Tracing] Introduce HeapDumpWriter helper class

base/trace_event/process_memory_dump.cc

Index: base/trace_event/process_memory_dump.cc
diff --git a/base/trace_event/process_memory_dump.cc b/base/trace_event/process_memory_dump.cc
index 0a7ca6d6153765ef6640147cd64d1ed42985aa8a..626a17aacea594a5379f4958c8ca77eab83f8889 100644
--- a/base/trace_event/process_memory_dump.cc
+++ b/base/trace_event/process_memory_dump.cc
@@ -145,6 +145,12 @@ MemoryAllocatorDump* ProcessMemoryDump::GetSharedGlobalAllocatorDump(
   return GetAllocatorDump(GetSharedGlobalAllocatorDumpName(guid));
 }
 
+void ProcessMemoryDump::AddHeapDump(const std::string& absolute_name,
+                                    scoped_refptr<TracedValue> heap_dump) {
+  DCHECK_EQ(0ul, heap_dumps_.count(absolute_name));
+  heap_dumps_[absolute_name] = heap_dump;
+}
+
 void ProcessMemoryDump::Clear() {
   if (has_process_totals_) {
     process_totals_.Clear();
@@ -159,6 +165,7 @@ void ProcessMemoryDump::Clear() {
   allocator_dumps_storage_.clear();
   allocator_dumps_.clear();
   allocator_dumps_edges_.clear();
+  heap_dumps_.clear();
 }
 
 void ProcessMemoryDump::TakeAllDumpsFrom(ProcessMemoryDump* other) {
@@ -180,6 +187,9 @@ void ProcessMemoryDump::TakeAllDumpsFrom(ProcessMemoryDump* other) {
                                 other->allocator_dumps_edges_.begin(),
                                 other->allocator_dumps_edges_.end());
   other->allocator_dumps_edges_.clear();
+
+  heap_dumps_.insert(other->heap_dumps_.begin(), other->heap_dumps_.end());
+  other->heap_dumps_.clear();
 }
 
 void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
@@ -202,6 +212,13 @@ void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
     value->EndDictionary();
   }
 
+  if (heap_dumps_.size() > 0) {
+    value->BeginDictionary("heaps");
+    for (const auto& name_and_dump : heap_dumps_)
+      value->SetValueWithCopiedName(name_and_dump.first, *name_and_dump.second);
+    value->EndDictionary();  // "heaps"
+  }
+
   value->BeginArray("allocators_graph");
   for (const MemoryAllocatorDumpEdge& edge : allocator_dumps_edges_) {
     value->BeginDictionary();