nearby: use performance.now() over Date() object

Similar to using base::TimeTicks over base::Time, performance.now() only ticks forward and allows us to not worry about system time changes.
It also allows for easier mock in tests.

Bug: 1156229
Test: browser_tests --gtest_filter=*NearbySh*
Change-Id: Id1cf98d77b5f3557aaa95daf8a3114714ef97008
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587613
Commit-Queue: Joon Ahn <joonbug@chromium.org>
Reviewed-by: James Vecore <vecore@google.com>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836769}

chrome/browser/resources/settings/chromeos/nearby_share_page/nearby_share_high_visibility_page.js

@@ -23,8 +23,8 @@ Polymer({
     },
 
     /**
-     * Timestamp in milliseconds since unix epoch of when high visibility will
-     * be turned off.
+     * DOMHighResTimeStamp in milliseconds of when high visibility will be
+     * turned off.
      * @type {number}
      */
     shutoffTimestamp: {
@@ -64,8 +64,7 @@ Polymer({
 
   /** @private */
   calculateRemainingTime_() {
-    const now = new Date().getTime();
-
+    const now = performance.now();
     const remainingTimeInMs =
         this.shutoffTimestamp > now ? this.shutoffTimestamp - now : 0;
     this.remainingTimeInSeconds_ = Math.trunc(remainingTimeInMs / 1000);

chrome/browser/resources/settings/chromeos/nearby_share_page/nearby_share_receive_dialog.js

@@ -130,7 +130,8 @@ Polymer({
    * @param {boolean} inHighVisibility
    */
   onHighVisibilityChanged(inHighVisibility) {
-    const now = new Date().getTime();
+    const now = performance.now();
+
     if (inHighVisibility === false &&
         now < this.highVisibilityShutoffTimestamp_) {
       // TODO(crbug/1134745): Exiting high visibility can happen for multiple
@@ -254,9 +255,9 @@ Polymer({
       return;
     }
 
-    // Date().getTime() returns current time in milliseconds since unix epoch.
+    // performance.now() returns DOMHighResTimeStamp in milliseconds.
     this.highVisibilityShutoffTimestamp_ =
-        new Date().getTime() + (shutoffTimeoutInSeconds * 1000);
+        performance.now() + (shutoffTimeoutInSeconds * 1000);
 
     // Register a receive surface to enter high visibility and show the page.
     this.receiveManager_.registerForegroundReceiveSurface();

chrome/test/data/webui/settings/chromeos/nearby_share_subpage_tests.js

@@ -254,6 +254,12 @@ suite('NearbyShare', function() {
   });
 
   test('show high visibility dialog', function() {
+    // Mock performance.now to return a constant 0 for testing.
+    const originalNow = performance.now;
+    performance.now = () => {
+      return 0;
+    };
+
     const params = new URLSearchParams;
     params.append('receive', '1');
     params.append('timeout', '600');  // 10 minutes
@@ -266,6 +272,9 @@ suite('NearbyShare', function() {
 
     const highVisibilityDialog = dialog.$$('nearby-share-high-visibility-page');
     assertTrue(test_util.isVisible(highVisibilityDialog));
-    assertGT(highVisibilityDialog.shutoffTimestamp, new Date().getTime());
+    assertEquals(highVisibilityDialog.shutoffTimestamp, 600 * 1000);
+
+    // Restore mock
+    performance.now = originalNow;
   });
 });