[Tracing] Make heap profiler type info a string

base/trace_event/heap_profiler_type_name_deduplicator.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/heap_profiler_type_name_deduplicator.h"
+
+#include <stdlib.h>
+#include <string>
+#include <utility>
+
+#include "base/json/string_escape.h"
+#include "base/strings/stringprintf.h"
+#include "base/trace_event/trace_event_memory_overhead.h"
+
+namespace base {
+namespace trace_event {
+
+TypeNameDeduplicator::TypeNameDeduplicator() {
+  // A null pointer has type ID 0 ("unknown type");
+  type_ids_.insert(std::make_pair(nullptr, 0));
+}
+
+TypeNameDeduplicator::~TypeNameDeduplicator() {}
+
+int TypeNameDeduplicator::Insert(const char* type_name) {
+  auto result = type_ids_.insert(std::make_pair(type_name, 0));
+  auto& elem = result.first;
+  bool did_not_exist_before = result.second;
+
+  if (did_not_exist_before) {
+    // The type IDs are assigned sequentially and they are zero-based, so
+    // |size() - 1| is the ID of the new element.
+    elem->second = static_cast<int>(type_ids_.size() - 1);
+  }
+
+  return elem->second;
+}
+
+void TypeNameDeduplicator::AppendAsTraceFormat(std::string* out) const {
+  out->append("{");  // Begin the type names dictionary.
+
+  auto it = type_ids_.begin();
+  std::string buffer;
+
+  // Write the first entry manually; the null pointer must not be dereferenced.
+  // (The first entry is the null pointer because a |std::map| is ordered.)
+  it++;
+  out->append("\"0\":\"[unknown]\"");
+
+  for (; it != type_ids_.end(); it++) {
+    // Type IDs in the trace are strings, write them as stringified keys of
+    // a dictionary.
+    SStringPrintf(&buffer, ",\"%d\":", it->second);
+
+    // |EscapeJSONString| appends, it does not overwrite |buffer|.
+    bool put_in_quotes = true;
+    EscapeJSONString(it->first, put_in_quotes, &buffer);
+    out->append(buffer);
+  }
+
+  out->append("}");  // End the type names dictionary.
+}
+
+void TypeNameDeduplicator::EstimateTraceMemoryOverhead(
+    TraceEventMemoryOverhead* overhead) {
+  // The size here is only an estimate; it fails to take into account the size
+  // of the tree nodes for the map, but as an estimate this should be fine.
+  size_t map_size = type_ids_.size() * sizeof(std::pair<const char*, int>);
+
+  overhead->Add("TypeNameDeduplicator",
+                sizeof(TypeNameDeduplicator) + map_size);
+}
+
+}  // namespace trace_event
+}  // namespace base