Web Inspector: heap snapshot: implement Distance column in Object's retaining tree.

Web Inspector: heap snapshot: implement Distance column in Object's retaining tree.
https://bugs.webkit.org/show_bug.cgi?id=78113

Retaining path list was replaced with Retaining tree some time ago.
But it was not so useful when we want to track the retaining path from an object to a DOM Window node.

Drive by fix: sort doesn't work in retaining tree panel.
Drive by fix: save/load child nodes doesn't work for the retaining tree panel.

Reviewed by Yury Semikhatsky.

* inspector/front-end/DetailedHeapshotGridNodes.js:
(WebInspector.HeapSnapshotObjectNode):
(WebInspector.HeapSnapshotObjectNode.prototype._childHashForEntity): save/load children fix
(WebInspector.HeapSnapshotObjectNode.prototype._childHashForNode): save/load children fix
(WebInspector.HeapSnapshotObjectNode.prototype.comparator):
(WebInspector.HeapSnapshotObjectNode.prototype._enhanceData):
* inspector/front-end/DetailedHeapshotView.js:
(WebInspector.HeapSnapshotContainmentDataGrid):
(WebInspector.HeapSnapshotRetainmentDataGrid):
(WebInspector.HeapSnapshotRetainmentDataGrid.prototype._sortFields):
* inspector/front-end/HeapSnapshot.js:
(WebInspector.HeapSnapshotRetainerEdge.prototype.set retainerIndex):
(WebInspector.HeapSnapshotRetainerEdge.prototype.set edgeIndex):
(WebInspector.HeapSnapshotRetainerEdge.prototype.get _node):
(WebInspector.HeapSnapshotRetainerEdge.prototype.get _edge):
(WebInspector.HeapSnapshotNode.prototype.get distanceToWindow):
(WebInspector.HeapSnapshot.prototype._init):
(WebInspector.HeapSnapshot.prototype._buildRetainers):
(WebInspector.HeapSnapshot.prototype._calculateObjectToWindowDistance):
(WebInspector.HeapSnapshot.prototype._bfs):
(WebInspector.HeapSnapshotEdgesProvider.prototype._serialize):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort.compareEdgeFieldName):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort.compareNodeField):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort.compareEdgeAndNode):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort.compareNodeAndEdge):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort.compareNodeAndNode):
(WebInspector.HeapSnapshotEdgesProvider.prototype.sort):
(WebInspector.HeapSnapshotNodesProvider.prototype._serialize):
* inspector/front-end/heapProfiler.css:
(.detailed-heapshot-view .data-grid td.distanceToWindow-column):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107106 268f45cc-cd09-0410-ab3c-d52691b4dbfc