Begin defining Extension-based Notebook Provider (#3172)

Implements provider contribution in the MainThreadNotebook, with matching function calls in the ExtHostNotebook class. This will allow us to proxy through notebook providers (specifically, creation of a notebook manager with required content, server managers) from an extension up through to the main process.

Implemented in this PR:
- Callthroughs for content and server manager APIs
- Very basic unit tests covering provider & manager registration

Not implemented:
- Fuller unit tests on the specific callthrough methods for content & server manager.
- Contribution point needed to test this (so we can actually pass through the extension's existing Notebook implementation)

src/sql/services/notebook/localContentManager.ts

@@ -4,29 +4,33 @@
  *--------------------------------------------------------------------------------------------*/
 
 'use strict';
+
 import { nb } from 'sqlops';
 
 import * as json from 'vs/base/common/json';
 import * as pfs from 'vs/base/node/pfs';
+import URI from 'vs/base/common/uri';
 
 import ContentManager = nb.ContentManager;
 import INotebook = nb.INotebook;
 
 export class LocalContentManager implements ContentManager {
-    public async getNotebookContents(path: string): Promise<INotebook> {
-        if (!path) {
+    public async getNotebookContents(notebookUri: URI): Promise<INotebook> {
+        if (!notebookUri) {
             return undefined;
         }
+        // TODO validate this is an actual file URI, and error if not
+        let path = notebookUri.fsPath;
         // Note: intentionally letting caller handle exceptions
         let notebookFileBuffer = await pfs.readFile(path);
         return <INotebook>json.parse(notebookFileBuffer.toString());
     }
 
-    public async save(path: string, notebook: INotebook): Promise<INotebook> {
+    public async save(notebookUri: URI, notebook: INotebook): Promise<INotebook> {
         // Convert to JSON with pretty-print functionality
         let contents = JSON.stringify(notebook, undefined, '    ');
+        let path = notebookUri.fsPath;
         await pfs.writeFile(path, contents);
         return notebook;
     }
-
 }