[tracing] Expose AddOwnershipEdge and CreateAllocatorDump with guid to blink. (blink-side).

public/platform/WebMemoryAllocatorDump.h

 // 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 WebMemoryAllocatorDump_h
 #define WebMemoryAllocatorDump_h
 
 #include "WebCommon.h"
 #include "WebString.h"
 
 namespace blink {
+typedef uint64_t WebMemoryAllocatorDumpGuid;
 
 // A container which holds all the attributes of a particular dump for a given
 // allocator.
 class BLINK_PLATFORM_EXPORT WebMemoryAllocatorDump {
 public:
     virtual ~WebMemoryAllocatorDump();
 
     // Adds a scalar attribute to the dump.
     // Arguments:
     //   name: name of the attribute. Typical names, emitted by most allocators
     //       dump providers are: "size" and "objects_count".
     //   units: the units for the attribute. Gives a hint to the trace-viewer UI
     //       about the semantics of the attribute.
     //       Currently supported values are "bytes" and "objects".
     //   value: the value of the attribute.
     virtual void AddScalar(const char* name, const char* units, uint64_t value) { }
     virtual void AddScalarF(const char* name, const char* units, double value) { }
     virtual void AddString(const char* name, const char* units, const WebString& value) { }
+
+    // |guid| is an optional global dump identifier, unique across all processes
+    // within the scope of a global dump. It is only required when using the
+    // graph APIs (see AddOwnershipEdge) to express retention / suballocation or
+    // cross process sharing. See crbug.com/492102 for design docs.
+    // Subsequent MemoryAllocatorDump(s) with the same |absolute_name| are
+    // expected to have the same guid.
+    virtual WebMemoryAllocatorDumpGuid guid() const
+    {
+        BLINK_ASSERT_NOT_REACHED();
+        return 0;
+    }
 };
 
 } // namespace blink
 
 #endif // WebMemoryAllocatorDump_h