Web Inspector: ResourceContentView.js incorrectly contains call to WebInspector.UIStr...

Web Inspector: ResourceContentView.js incorrectly contains call to WebInspector.UIString with a variable parameter
https://bugs.webkit.org/show_bug.cgi?id=140268

Reviewed by Timothy Hatcher.

UIString no longer incorrectly used around variables. Drive-by fixes to prototype inheritance style.
Use of Promises corrected such that requesting content for a resource resolves rather than rejects if
a resource can't be found or has another error that isn't a web inspector error.

* Localizations/en.lproj/localizedStrings.js: Updated.
* UserInterface/Models/Resource.js: Change reject to resolve.
* UserInterface/Models/Script.js:
(WebInspector.Script.prototype.requestContentFromBackend): Proper use of Error object.
* UserInterface/Models/SourceCode.js: Use correct inheritance style.
* UserInterface/Views/ResourceContentView.js:
(WebInspector.ResourceContentView.prototype._contentAvailable): Handle error now that promise resolves.
(WebInspector.ResourceContentView.prototype._contentError): Remove incorrect use of UIString.
* UserInterface/Views/SourceCodeTextEditor.js:
(WebInspector.SourceCodeTextEditor.prototype._contentAvailable): Handle error now that promise resolves.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@178970 268f45cc-cd09-0410-ab3c-d52691b4dbfc