feat(multiple): Minor additions (angular#2921)

* Increase the accuracy of performance marks, by leaning on Zone's start marker
* Add automatic transfer state support to the getDownloadURL pipe
* Storage.child type fix

Author: jamesdaniels

src/compat/performance/performance.service.ts

@@ -2,27 +2,16 @@ import { ApplicationRef, Injectable, OnDestroy } from '@angular/core';
 import { Subscription } from 'rxjs';
 import { first, tap } from 'rxjs/operators';
 
-const IS_STABLE_START_MARK = '_isStableStart';
+const IS_STABLE_START_MARK = 'Zone';
 const IS_STABLE_END_MARK = '_isStableEnd';
 
-function markStarts() {
-    if (typeof(window) !== 'undefined' && window.performance && window.performance.mark) {
-        window.performance.mark(IS_STABLE_START_MARK);
-        return true;
-    } else {
-        return false;
-    }
-}
-
-const started = markStarts();
-
 @Injectable()
 export class PerformanceMonitoringService implements OnDestroy {
 
     private disposable: Subscription|undefined;
 
     constructor(appRef: ApplicationRef) {
-        if (started && window.performance.mark) {
+        if (typeof window !== 'undefined' && window.performance?.mark) {
             this.disposable = appRef.isStable.pipe(
                 first(it => it),
                 tap(() => {

src/compat/performance/performance.ts

@@ -52,7 +52,7 @@ export class AngularFirePerformance {
 }
 
 const trace$ = (traceId: string) => {
-  if (typeof window !== 'undefined' && window.performance && window.performance.mark) {
+  if (typeof window !== 'undefined' && window.performance?.mark) {
     const entries = window.performance.getEntriesByName(traceId, 'measure') || [];
     const startMarkName = `_${traceId}Start[${entries.length}]`;
     const endMarkName = `_${traceId}End[${entries.length}]`;

src/compat/storage/pipes/storageUrl.pipe.ts

@@ -1,6 +1,8 @@
 import { AsyncPipe } from '@angular/common';
-import { ChangeDetectorRef, NgModule, OnDestroy, Pipe, PipeTransform } from '@angular/core';
-import { Observable } from 'rxjs';
+import { ChangeDetectorRef, NgModule, OnDestroy, Optional, Pipe, PipeTransform } from '@angular/core';
+import { makeStateKey, TransferState } from '@angular/platform-browser';
+import { Observable, of } from 'rxjs';
+import { tap } from 'rxjs/operators';
 import { AngularFireStorage } from '../storage';
 
 /** to be used with in combination with | async */
@@ -14,14 +16,22 @@ export class GetDownloadURLPipe implements PipeTransform, OnDestroy {
   private path: string;
   private downloadUrl$: Observable<any>;
 
-  constructor(private storage: AngularFireStorage, cdr: ChangeDetectorRef) {
+  constructor(
+    private storage: AngularFireStorage,
+    cdr: ChangeDetectorRef,
+    @Optional() private state: TransferState
+  ) {
     this.asyncPipe = new AsyncPipe(cdr);
   }
 
   transform(path: string) {
     if (path !== this.path) {
       this.path = path;
-      this.downloadUrl$ = this.storage.ref(path).getDownloadURL();
+      const key = makeStateKey<string>(`|getDownloadURL|${path}`);
+      const existing = this.state?.get(key, undefined);
+      this.downloadUrl$ = existing ? of(existing) : this.storage.ref(path).getDownloadURL().pipe(
+        tap(it => this.state?.set(key, it))
+      );
     }
     return this.asyncPipe.transform(this.downloadUrl$);
   }

src/compat/storage/ref.ts

@@ -8,7 +8,7 @@ export interface AngularFireStorageReference {
   getDownloadURL(): Observable<any>;
   getMetadata(): Observable<any>;
   delete(): Observable<any>;
-  child(path: string): any;
+  child(path: string): AngularFireStorageReference;
   updateMetadata(meta: SettableMetadata): Observable<any>;
   put(data: any, metadata?: UploadMetadata | undefined): AngularFireUploadTask;
   putString(data: string, format?: string | undefined, metadata?: UploadMetadata | undefined): AngularFireUploadTask;