Add JS heap snapshotting functionality to Telemetry (part 2)

tools/telemetry/telemetry/core/heap/retaining_edge.py

Index: tools/telemetry/telemetry/core/heap/retaining_edge.py
diff --git a/tools/telemetry/telemetry/core/heap/retaining_edge.py b/tools/telemetry/telemetry/core/heap/retaining_edge.py
new file mode 100644
index 0000000000000000000000000000000000000000..d6b9978ce6a12a5d4f287459b665cd42f10d7ab1
--- /dev/null
+++ b/tools/telemetry/telemetry/core/heap/retaining_edge.py
@@ -0,0 +1,52 @@
+# Copyright 2013 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.
+
+class RetainingEdge(object):
+  """Data structure for representing a retainer relationship between objects.
+
+  Attributes:
+    from_object_id: int, id of the object which is the start point of this
+        RetainingEdge.  Used when the corresponding LiveHeapObject object is not
+        yet contstructed.
+    to_object_id: int, id of the object which is the end point of this
+        RetainingEdge. Used when the corresponding LiveHeapObject object is not
+        yet contstructed.
+    from_object: LiveHeapObject, the start point of this RetainingEdge.
+    to_object: LiveHeapObject, the end point of this RetainingEdge.
+    type_string: str, the type of the RetainingEdge.
+    name_string: str, the JavaScript attribute name this RetainingEdge
+        represents.
+  """
+
+  def __init__(self, from_object_id, to_object_id, type_string, name_string):
+    """Initializes the RetainingEdge object.
+
+    Args:
+      from_object_id: int, id of the object which is the start point of this
+          RetainingEdge. Used when the corresponding LiveHeapObject object is
+          not yet contstructed.
+      to_object_id: int, id of the object which is the end point of this
+          RetainingEdge. Used when the corresponding LiveHeapObject object is
+          not yet contstructed.
+      type_string: str, the type of the RetainingEdge.
+      name_string: str, the JavaScript attribute name this RetainingEdge
+          represents.
+    """
+    self.from_object_id = from_object_id
+    self.to_object_id = to_object_id
+    self.from_object = {}
+    self.to_object = {}
+    self.type_string = type_string
+    self.name_string = name_string
+
+  def SetFromObject(self, obj):
+    self.from_object = obj
+    return self
+
+  def SetToObject(self, obj):
+    self.to_object = obj
+    return self
+
+  def __str__(self):
+    return 'RetainingEdge(' + self.type_string + ' ' + self.name_string + ')'