Add a constant for 'current'

Change-Id: I0560601fefe723de01817c0b5fde3576dcd0d2ef
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
index 51ce9b4..20fbc32 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
@@ -42,6 +42,7 @@
 import {
   fetchChangeUpdates,
   patchNumEquals,
+  CURRENT,
 } from '../../../utils/patch-set-util';
 import {
   changeIsOpen,
@@ -1591,7 +1592,7 @@
     if (!labels) {
       return Promise.resolve(undefined);
     }
-    return this.$.restAPI.saveChangeReview(newChangeId, 'current', {labels});
+    return this.$.restAPI.saveChangeReview(newChangeId, CURRENT, {labels});
   }
 
   _handleResponse(action: UIActionInfo, response?: Response) {
diff --git a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
index 683d887..ef5be9fd 100644
--- a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
+++ b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
@@ -23,6 +23,7 @@
   getParentIndex,
   isMergeParent,
   patchNumEquals,
+  CURRENT,
 } from '../../../utils/patch-set-util';
 import {customElement, property} from '@polymer/decorators';
 import {
@@ -612,7 +613,7 @@
   }
 
   getPortedComments(changeNum: NumericChangeId, revision?: RevisionId) {
-    if (!revision) revision = 'current';
+    if (!revision) revision = CURRENT;
     return Promise.all([
       this.$.restAPI.getPortedComments(changeNum, revision),
       this.$.restAPI.getPortedDrafts(changeNum, revision),
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
index bb0ed61..5a6113c 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
@@ -48,6 +48,7 @@
   computeLatestPatchNum,
   patchNumEquals,
   PatchSet,
+  CURRENT,
 } from '../../../utils/patch-set-util';
 import {
   addUnmodifiedFiles,
@@ -1047,7 +1048,7 @@
 
     const portedCommentsPromise = this.$.commentAPI.getPortedComments(
       value.changeNum,
-      value.patchNum || 'current'
+      value.patchNum || CURRENT
     );
 
     const promises: Promise<unknown>[] = [];
diff --git a/polygerrit-ui/app/elements/shared/gr-hovercard-account/gr-hovercard-account.ts b/polygerrit-ui/app/elements/shared/gr-hovercard-account/gr-hovercard-account.ts
index da2881e..0b4e577 100644
--- a/polygerrit-ui/app/elements/shared/gr-hovercard-account/gr-hovercard-account.ts
+++ b/polygerrit-ui/app/elements/shared/gr-hovercard-account/gr-hovercard-account.ts
@@ -46,6 +46,7 @@
 } from '../../../utils/attention-set-util';
 import {ReviewerState} from '../../../constants/constants';
 import {isRemovableReviewer} from '../../../utils/change-util';
+import {CURRENT} from '../../../utils/patch-set-util';
 
 export interface GrHovercardAccount {
   $: {
@@ -186,7 +187,7 @@
     ];
 
     this.$.restAPI
-      .saveChangeReview(this.change._number, 'current', reviewInput)
+      .saveChangeReview(this.change._number, CURRENT, reviewInput)
       .then(response => {
         if (!response || !response.ok) {
           throw new Error(
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
index d75c186..b86fcff 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.js
@@ -22,6 +22,7 @@
 import {ListChangesOption} from '../../../utils/change-util.js';
 import {appContext} from '../../../services/app-context.js';
 import {createChange} from '../../../test/test-data-generators.js';
+import {CURRENT} from '../../../utils/patch-set-util.js';
 
 const basicFixture = fixtureFromElement('gr-rest-api-interface');
 
@@ -1350,7 +1351,7 @@
     sinon.stub(element._restApiHelper, 'fetchJSON').returns(Promise.resolve({
       ok: false}));
 
-    element.getPortedComments(change._number, 'current');
+    element.getPortedComments(change._number, CURRENT);
 
     assert.isFalse(dispatchStub.called);
   });
@@ -1361,7 +1362,7 @@
     const getChangeURLAndFetchStub = sinon.stub(element,
         '_getChangeURLAndFetch');
 
-    element.getPortedDrafts(change._number, 'current');
+    element.getPortedDrafts(change._number, CURRENT);
 
     assert.isFalse(getChangeURLAndFetchStub.called);
   });
diff --git a/polygerrit-ui/app/utils/patch-set-util.ts b/polygerrit-ui/app/utils/patch-set-util.ts
index 8974af8..d063168 100644
--- a/polygerrit-ui/app/utils/patch-set-util.ts
+++ b/polygerrit-ui/app/utils/patch-set-util.ts
@@ -45,6 +45,8 @@
   PARENT: 'PARENT',
 };
 
+export const CURRENT = 'current';
+
 export interface PatchSet {
   num: PatchSetNum;
   desc: string | undefined;