[Spaces] - Support "Recently viewed" widget (#22492)

[skip ci]
This PR makes the "Recently viewed" widget on the Kibana home page space-aware. The widget will only show saved objects that were viewed within the user's current space.

This is accomplished by changing the way the `RecentlyAccessed` module creates its `PersistedLog`. Previously, the `PersistedLog` was using a hard-coded key, but now it is deriving its key based off of the current `basePath`, which contains the space identifier.

I chose this approach because this code lies completely within OSS Kibana, and I did not want to make this module aware of the Spaces plugin. Spaces augments the `basePath` in order to function and construct space-aware links within the UI, so this ends up being transparent to consumers of `chrome.getBasePath`


You'll notice that the `PersistedLog` key is partially hashed. We do this because we don't want the browser to store information about which spaces a particular user may or may not have access to (see this [earlier conversation](#19417 (comment)))


### Important
Installations that have a configured `basePath` other than the default `''` will have their "Recently viewed" list cleared after upgrading to 6.5, because the basePath will become part of the `localStorage` key, when it previously wasn't. While this may _technically_ be a breaking change, I'm hoping this will be acceptable.

Fixes #21961

src/ui/public/persisted_log/create_log_key.js

@@ -0,0 +1,31 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { Sha256 } from '../crypto';
+
+export function createLogKey(type, optionalIdentifier) {
+  const baseKey = `kibana.history.${type}`;
+
+  if (!optionalIdentifier) {
+    return baseKey;
+  }
+
+  const protectedIdentifier = new Sha256().update(optionalIdentifier, 'utf8').digest('base64');
+  return `${baseKey}-${protectedIdentifier}`;
+}

src/ui/public/persisted_log/create_log_key.test.js

@@ -0,0 +1,35 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { createLogKey } from './create_log_key';
+
+describe('createLogKey', () => {
+  it('should create a key starting with "kibana.history"', () => {
+    expect(createLogKey('foo', 'bar')).toMatch(/^kibana\.history/);
+  });
+
+  it('should include a hashed suffix of the identifier when present', () => {
+    const expectedSuffix = `/N4rLtula/QIYB+3If6bXDONEO5CnqBPrlURto+/j7k=`;
+    expect(createLogKey('foo', 'bar')).toMatch(`kibana.history.foo-${expectedSuffix}`);
+  });
+
+  it('should not include a hashed suffix if the identifier is not present', () => {
+    expect(createLogKey('foo')).toEqual('kibana.history.foo');
+  });
+});

src/ui/public/persisted_log/persisted_log.test.js

@@ -22,6 +22,12 @@ import sinon from 'sinon';
 import expect from 'expect.js';
 import { PersistedLog } from './';
 
+jest.mock('../chrome', () => {
+  return {
+    getBasePath: () => `/some/base/path`
+  };
+});
+
 const historyName = 'testHistory';
 const historyLimit = 10;
 const payload = [

src/ui/public/persisted_log/recently_accessed.js

@@ -16,8 +16,9 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-
+import chrome from '../chrome';
 import { PersistedLog } from './';
+import { createLogKey } from './create_log_key';
 
 class RecentlyAccessed {
   constructor() {
@@ -28,7 +29,8 @@ class RecentlyAccessed {
         return oldItem.id === newItem.id;
       }
     };
-    this.history = new PersistedLog('kibana.history.recentlyAccessed', historyOptions);
+    const logKey = createLogKey('recentlyAccessed', chrome.getBasePath());
+    this.history = new PersistedLog(logKey, historyOptions);
   }
 
   add(link, label, id) {