Merge pull request #528 from ipfs-shipyard/fix/linkify-tree-check

Linkify fix to run safety checks on entire parent tree

## Background

Linkify is an opt-in experiment on _Preferences_ screen:
https://ipfs.io/ipfs/QmY1D42peN9oPCoEeFezKR2jWKReDnJek52zcj7pcXXaaH

## In This PR

A lot of web-based text editors create elaborate DOM trees and together with @lgierth  we've experienced it first hand that  it is not enough to check if parent is safe for linkification. 

This change walks back over entire parent tree to ensure none of parents
has a no-go flag for linkification (eg. HTMLElement.contentEditable property)

Test pages:
- https://ipfs.io/ipfs/bafybeidvtwx54qr44kidymvhfzefzxhgkieigwth6oswk75zhlzjdmunoy/linkify-demo.html
- https://hackmd.io/kMlFFc_bQoiabAul5RjYag?both#
  - Left pane (editor) will be ignored after this PR is merged. Right now, if multiple people edit the same line, content gets destroyed.

add-on/src/contentScripts/linkifyDOM.js

@@ -139,16 +139,28 @@ const PQueue = require('p-queue')
     return window.ipfsCompanionLinkifyValidationCache.get(path)
   }
 
-  async function linkifyTextNode (node) {
-    const parent = node.parentNode
+  function isParentTreeSafe (node) {
+    let parent = node.parentNode
     // Skip if no longer in visible DOM
-    if (!parent) return
-    // Skip already linkified nodes
-    if (parent.className && parent.className.match(/\blinkifiedIpfsAddress\b/)) return
-    // Skip styled <pre> -- often highlighted by script.
-    if (parent.tagName === 'PRE' && parent.className) return
-    // Skip forms, textareas
-    if (parent.isContentEditable) return
+    if (!parent) return false
+    // Walk back over parent tree and check each of them
+    while (parent) {
+      // Skip forms, textareas
+      if (parent.isContentEditable) return false
+      // Skip already linkified nodes
+      if (parent.className && parent.className.match(/\blinkifiedIpfsAddress\b/)) return false
+      // Skip styled <pre> -- often highlighted by scripts
+      if (parent.tagName === 'PRE' && parent.className) return false
+      // Skip if no longer in visible DOM
+      if (!(parent instanceof HTMLDocument) && !parent.parentNode) return false
+      parent = parent.parentNode
+    }
+    return true
+  }
+
+  async function linkifyTextNode (node) {
+    // Skip if node belongs to a parent from unsafe tree
+    if (!isParentTreeSafe(node)) return
 
     let link
     let match