[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_event_writer.h

Index: base/trace_event/heap_profiler_event_writer.h
diff --git a/base/trace_event/heap_profiler_event_writer.h b/base/trace_event/heap_profiler_event_writer.h
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index 0000000000000000000000000000000000000000..3c827c29cb8947f681b831a85c5f153de7a4644a
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+++ b/base/trace_event/heap_profiler_event_writer.h
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+// 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.
+
+#ifndef BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_
+#define BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_
+
+#include <stddef.h>
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+#include "base/base_export.h"
+
+/*
+  Heap profile event data format.
+
+  Input is:
+    1. Per allocator AllocationRegister
+    2. Per process deduplicators (for stack frames, types, strings)
+
+  Formatting event data is done in two steps:
+    1. Call SerializeHeapDump() on allocation registers and accumulate
+       results in SerializedHeapDumpsMap. SerializeHeapDump() exports
+       allocation register as "allocators/<allocator>" dictionary outlined
+       below; serialization uses deduplicators from MemoryDumpSessionState.
+    2. Call SerializeHeapProfileEventData() with SerializedHeapDumpsMap and
+       MemoryDumpSessionState. This puts everything together:
+       a. Entries from SerializedHeapDumpsMap are formatted as
+          "allocators/<allocator>" nodes.
+       b. Deduplicators from MemoryDumpSessionState are formatted as
+          "maps/" nodes. Deduplicators are exported incrementally using
+          their ExportIncrementally() methods.
+
+  SerializeHeapDump() aggregates allocation register entries first by backtrace,
+  then by type (i.e. creates map {(backtrace, type) -> AllocationMetrics}).
+  During aggregation backtraces and types are deduplicated.
+
+  Resulting event data format:
+  {
+    "version": 1,
+
+    "allocators": {
+      ["malloc", "partition_alloc", "blinkgc"]: {
+        "nodes":  [<stack_frame_id1>, <stack_frame_id2>, ...],
+        "types":  [<type_id1>,        <type_id2>,        ...],
+        "counts": [<count1>,          <count2>,          ...],
+        "sizes":  [<size1>,           <size2>,           ...]
+      }
+    },
+
+    "maps": {
+      "nodes": [
+        {
+          "id": <stack_frame_id>,
+          "parent": <parent_id>,
+          "name_sid": <name_string_id>
+        },
+        ...
+      ],
+      "types": [
+        {
+          "id": <type_id>,
+          "name_sid": <name_string_id>
+        }
+      ],
+      "strings": [
+        {
+          "id": <string_id>,
+          "string": <string>
+        }
+      ]
+    }
+  }
+*/
+
+namespace base {
+namespace trace_event {
+
+class AllocationRegister;
+class MemoryDumpSessionState;
+class TracedValue;
+
+// Exports heap allocations as "allocators/<allocator>" dictionary described
+// above. Return value is supposed to be added to SerializedHeapDumpsMap map
+// and later passed to SerializeHeapProfileEventData().
+BASE_EXPORT std::unique_ptr<TracedValue> SerializeHeapDump(
+    const AllocationRegister& allocation_register,
+    const MemoryDumpSessionState& session_state);
+
+// Maps allocator name to its heap dump.
+using SerializedHeapDumpsMap =
+    std::unordered_map<std::string, std::unique_ptr<TracedValue>>;
+
+// Exports event data according to the format described above.
+BASE_EXPORT std::unique_ptr<TracedValue> SerializeHeapProfileEventData(
+    const SerializedHeapDumpsMap& heap_dumps,
+    const MemoryDumpSessionState& session_state);
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_