Currently, each time parent_index() is invoked, two depth-first searches
are incurred to find the node's parent and grandparent. This becomes
particularly expensive, for example, when trying to scroll through a
large <ul> list.
Instead, upon creation, traverse the DOM JSON and create a map of child
nodes to their parent. Then those two lookups become hash map lookups
rather than a DFS traversal.
Currently, the DOM Inspector stores a numeric ID for each DOM node. This
is used to look up the data for that node in the JSON representation of
the DOM. The method to do this search performs a depth-first search
through the JSON value, and is invoked quite frequently.
Instead, we can just store a pointer to the JSON value in the index, and
avoid this search altogether. This is similar to how the IPWV stores a
pointer to the DOM node.
To improve the performance of the DOM Inspector when the Browser is run
in multi-process mode, do not create copies of the JSON values sent via
IPC when searching for a model index. Methods that are guaranteed to
return a value now return a reference. Methods that do not have such a
guarantee return a pointer (rather than an Optional, because Optional
cannot hold references).
The DOM Inspector performs well at first, but will start lagging again
once the tree is expanded a few nodes deep and/or with many nodes
visible in the tree.
This introduces a new DOMTreeJSONModel, which provides the Model for the
InspectorWidget when the Browser is running using the
OutOfProcessWebView.
This Model is constructed with a JSON object received via IPC from the
WebContentServer.
