[tracing] Expose memory-infra tracing infrastructure to Blink.

public/platform/WebProcessMemoryDump.h

Index: public/platform/WebProcessMemoryDump.h
diff --git a/public/platform/WebProcessMemoryDump.h b/public/platform/WebProcessMemoryDump.h
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+// 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.
+
+#ifndef WebProcessMemoryDump_h
+#define WebProcessMemoryDump_h
+
+#include "WebNonCopyable.h"
+#include "WebString.h"
+
+namespace blink {
+
+class WebMemoryAllocatorDump;
+
+// A container which holds all the dumps for the various allocators for a given process.
+// Embedders of WebMemoryDumpProvider are expected to populate a WebProcessMemoryDump instance with
+// the stats of their allocators.
+class BLINK_PLATFORM_EXPORT WebProcessMemoryDump : public WebNonCopyable {
+public:
+    // Creates a new MemoryAllocatorDump with the given name and returns the empty object back to
+    // the caller. |absoluteName| uniquely identifies the the dump within the scope of a
+    // ProcessMemoryDump. It is possible to express nesting by means of a slash-separated path
+    // semantic (e.g., "allocator_name/arena-1/sub-heap-X").
+    virtual WebMemoryAllocatorDump* createMemoryAllocatorDump(const WebString& absoluteName)
+    {
+        return nullptr;
+    }
+};
+
+} // namespace blink
+
+#endif // WebProcessMemoryDump_h