[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_string_deduplicator.cc

Index: base/trace_event/heap_profiler_string_deduplicator.cc
diff --git a/base/trace_event/heap_profiler_string_deduplicator.cc b/base/trace_event/heap_profiler_string_deduplicator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bf035a19c03044b5cf675d77caa85ff65ea292db
--- /dev/null
+++ b/base/trace_event/heap_profiler_string_deduplicator.cc
@@ -0,0 +1,58 @@
+// Copyright 2017 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_string_deduplicator.h"
+
+#include "base/trace_event/memory_usage_estimator.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_argument.h"
+#include "base/trace_event/trace_event_memory_overhead.h"
+
+namespace base {
+namespace trace_event {
+
+StringDeduplicator::StringDeduplicator() : last_serialized_index_(0) {
+  // Add implicit entry for id 0 (NULL strings).
+  strings_.push_back("[null]");
+}
+
+StringDeduplicator::~StringDeduplicator() {}
+
+int StringDeduplicator::Insert(StringPiece string) {
+  if (!string.data()) {
+    // NULL strings are mapped to id 0.
+    return 0;
+  }
+  auto it = string_ids_.find(string);
+  if (it != string_ids_.end())
+    return it->second;
+
+  // Insert new mapping. Note that |string_ids_| keys reference values
+  // from |strings_|.
+  int string_id = static_cast<int>(strings_.size());
+  strings_.push_back(string.as_string());
+  auto iter_and_flag = string_ids_.insert({strings_.back(), string_id});
+  DCHECK(iter_and_flag.second);  // insert() must succeed
+  return string_id;
+}
+
+void StringDeduplicator::SerializeIncrementally(TracedValue* traced_value) {
+  for (; last_serialized_index_ != strings_.size(); ++last_serialized_index_) {
+    traced_value->BeginDictionary();
+    traced_value->SetInteger("id", last_serialized_index_);
+    traced_value->SetString("string", strings_[last_serialized_index_]);
+    traced_value->EndDictionary();
+  }
+}
+
+void StringDeduplicator::EstimateTraceMemoryOverhead(
+    TraceEventMemoryOverhead* overhead) {
+  size_t memory_usage =
+      EstimateMemoryUsage(string_ids_) + EstimateMemoryUsage(strings_);
+  overhead->Add(TraceEventMemoryOverhead::kHeapProfilerStringDeduplicator,
+                sizeof(StringDeduplicator) + memory_usage);
+}
+
+}  // namespace trace_event
+}  // namespace base