Notify user when crypto data is missing

If we have account data in local storage but nothing in the crypto store, it
generally means the browser has evicted IndexedDB out from under us. This adds a
modal to explain the situation and offer to completely clear storage to get
things back to normal.

Fixes https://github.com/vector-im/riot-web/issues/9109

src/components/views/dialogs/StorageEvictedDialog.js

@@ -0,0 +1,77 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed 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 React from 'react';
+import PropTypes from 'prop-types';
+import sdk from '../../../index';
+import SdkConfig from '../../../SdkConfig';
+import Modal from '../../../Modal';
+import { _t } from '../../../languageHandler';
+
+export default class StorageEvictedDialog extends React.Component {
+    static propTypes = {
+        onFinished: PropTypes.func.isRequired,
+    };
+
+    _sendBugReport = ev => {
+        ev.preventDefault();
+        const BugReportDialog = sdk.getComponent("dialogs.BugReportDialog");
+        Modal.createTrackedDialog('Storage evicted', 'Send Bug Report Dialog', BugReportDialog, {});
+    };
+
+    _onSignOutClick = () => {
+        this.props.onFinished(true);
+    };
+
+    render() {
+        const BaseDialog = sdk.getComponent('views.dialogs.BaseDialog');
+        const DialogButtons = sdk.getComponent('views.elements.DialogButtons');
+
+        let logRequest;
+        if (SdkConfig.get().bug_report_endpoint_url) {
+            logRequest = _t(
+                "To help us prevent this in future, please <a>send us logs</a>.", {},
+            {
+                a: text => <a href="#" onClick={this._sendBugReport}>{text}</a>,
+            });
+        }
+
+        return (
+            <BaseDialog className="mx_ErrorDialog" onFinished={this.props.onFinished}
+                title={_t('Missing session data')}
+                contentId='mx_Dialog_content'
+                hasCancel={false}
+            >
+                <div className="mx_Dialog_content" id='mx_Dialog_content'>
+                    <p>{_t(
+                        "Some session data, including encrypted message keys, is " +
+                        "missing. Sign out and sign in to fix this, restoring keys " +
+                        "from backup.",
+                    )}</p>
+                    <p>{_t(
+                        "Your browser likely removed this data when running low on " +
+                        "disk space.",
+                    )} {logRequest}</p>
+                </div>
+                <DialogButtons primaryButton={_t("Sign out")}
+                    onPrimaryButtonClick={this._onSignOutClick}
+                    focus={true}
+                    hasCancel={false}
+                />
+            </BaseDialog>
+        );
+    }
+}