[tracing] Introduce support for userland memory allocators dumps.

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 5363db559c32151712dc128e74d44f1933bbec00..131494e9856c822468e474647d16b68315363a4c 100644
--- a/base/trace_event/process_memory_dump.cc
+++ b/base/trace_event/process_memory_dump.cc
@@ -17,6 +17,27 @@ ProcessMemoryDump::ProcessMemoryDump()
 ProcessMemoryDump::~ProcessMemoryDump() {
 }
 
+MemoryAllocatorDump* ProcessMemoryDump::AddAllocatorDump(
+    const std::string& name) {
+  return AddAllocatorDump(name, nullptr);
+}
+
+MemoryAllocatorDump* ProcessMemoryDump::AddAllocatorDump(
+    const std::string& name,
+    MemoryAllocatorDump* parent) {
+  DCHECK_EQ(0ul, allocator_dumps_.count(name));
+  MemoryAllocatorDump* mad = new MemoryAllocatorDump(name, parent);
+  allocator_dumps_storage_.push_back(mad);
+  allocator_dumps_[name] = mad;
+  return mad;
+}
+
+MemoryAllocatorDump* ProcessMemoryDump::GetAllocatorDump(
+    const std::string& name) const {
+  auto it = allocator_dumps_.find(name);
+  return it == allocator_dumps_.end() ? nullptr : it->second;
+}
+
 void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
   // Build up the [dumper name] -> [value] dictionary.
   if (has_process_totals_) {
@@ -29,6 +50,12 @@ void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
     process_mmaps_.AsValueInto(value);
     value->EndDictionary();
   }
+  if (allocator_dumps_storage_.size() > 0) {
+    value->BeginDictionary("allocators");
+    for (const MemoryAllocatorDump* allocator_dump : allocator_dumps_storage_)
+      allocator_dump->AsValueInto(value);
+    value->EndDictionary();
+  }
 }
 
 }  // namespace trace_event