[Sources] Refactored component to use contents.id (#6184)
[Sources] Refactored component to use contents.id (#6184)

* Refactored ~/src/components/PrimaryPanes/SourceTree.js to use contents.id instead of contents.get("id").

* Scale back the scope of this PR

bomsy/debugger.html,jasonLaster/debugger.html,darkwing/debugger.html,jbhoosreddy/debugger.html,devtools-html/debugger.html,jbhoosreddy/debugger.html,wldcordeiro/debugger.html,jbhoosreddy/debugger.html,ruturajv/debugger.html,jasonLaster/debugger.html,bomsy/debugger.html,jbhoosreddy/debugger.html,bomsy/debugger.html,bomsy/debugger.html,darkwing/debugger.html,wldcordeiro/debugger.html,devtools-html/debugger.html,wldcordeiro/debugger.html,jbhoosreddy/debugger.html,wldcordeiro/debugger.html,bomsy/debugger.html,jasonLaster/debugger.html,wldcordeiro/debugger.html,jasonLaster/debugger.html,darkwing/debugger.html,devtools-html/debugger.html,darkwing/debugger.html,ruturajv/debugger.html,devtools-html/debugger.html,ruturajv/debugger.html,darkwing/debugger.html,bomsy/debugger.html,wldcordeiro/debugger.html,wldcordeiro/debugger.html,devtools-html/debugger.html,ruturajv/debugger.html,ruturajv/debugger.html,ruturajv/debugger.html,darkwing/debugger.html,jasonLaster/debugger.html,darkwing/debugger.html,bomsy/debugger.html,devtools-html/debugger.html,jasonLaster/debugger.html,jbhoosreddy/debugger.html,jbhoosreddy/debugger.html,jasonLaster/debugger.html,ruturajv/debugger.html,devtools-html/debugger.html