[google_font] Move the httpClient from a package level variable to the Config object

packages/google_fonts/lib/src/google_fonts_all_parts.dart

@@ -9,6 +9,7 @@
 import 'dart:ui' as ui;
 
 import 'package:flutter/material.dart';
+import 'package:http/http.dart' as http;
 
 import 'google_fonts_base.dart';
 import 'google_fonts_parts/part_a.dart';
@@ -44,6 +45,13 @@ class Config {
   /// Whether or not the GoogleFonts library can make requests to
   /// [fonts.google.com](https://fonts.google.com/) to retrieve font files.
   bool allowRuntimeFetching = true;
+
+  /// The HTTP client used to fetch fonts.
+  ///
+  /// If this is null, a shared default [http.Client] will be used.
+  ///
+  /// If you supply a client, you are responsible for closing it.
+  http.Client? httpClient;
 }
 
 /// Provides configuration, and static methods to obtain [TextStyle]s and [TextTheme]s.

packages/google_fonts/lib/src/google_fonts_base.dart

@@ -32,9 +32,8 @@ void clearCache() => _loadedFonts.clear();
 /// the [FontLoader], that future is removed from this set.
 final Set<Future<void>> pendingFontFutures = <Future<void>>{};
 
-/// The client used to fetch fonts.
-@visibleForTesting
-http.Client httpClient = http.Client();
+/// Default client used to fetch fonts when one is not supplied.
+final http.Client _httpClient = http.Client();
 
 /// The asset manifest to use for loading pre-bundled fonts.
 @visibleForTesting
@@ -260,8 +259,9 @@ Future<ByteData> _httpFetchFontAndSaveToDevice(
   }
 
   http.Response response;
+  final http.Client client = GoogleFonts.config.httpClient ?? _httpClient;
   try {
-    response = await httpClient.get(uri);
+    response = await client.get(uri);
   } catch (e) {
     throw Exception('Failed to load font with url ${file.url}: $e');
   }

packages/google_fonts/test/google_fonts_text_style_test.dart

@@ -57,9 +57,9 @@ void main() {
   late MockHttpClient mockHttpClient;
 
   setUp(() async {
-    mockHttpClient = MockHttpClient();
-    httpClient = mockHttpClient;
     assetManifest = MockAssetManifest();
+    mockHttpClient = MockHttpClient();
+    GoogleFonts.config.httpClient = mockHttpClient;
     GoogleFonts.config.allowRuntimeFetching = true;
     when(mockHttpClient.gets(any)).thenAnswer((_) async {
       return http.Response(_fakeResponse, 200);

packages/google_fonts/test/load_font_if_necessary_test.dart

@@ -116,9 +116,9 @@ void main() {
   late MockHttpClient mockHttpClient;
 
   setUp(() async {
-    mockHttpClient = MockHttpClient();
-    httpClient = mockHttpClient;
     assetManifest = MockAssetManifest();
+    mockHttpClient = MockHttpClient();
+    GoogleFonts.config.httpClient = mockHttpClient;
     GoogleFonts.config.allowRuntimeFetching = true;
     when(mockHttpClient.gets(any)).thenAnswer((_) async {
       return http.Response(_fakeResponse, 200);

packages/google_fonts/test/load_font_if_necessary_with_local_fonts_test.dart

@@ -76,9 +76,9 @@ void main() {
   late MockHttpClient mockHttpClient;
 
   setUp(() async {
-    mockHttpClient = MockHttpClient();
-    httpClient = mockHttpClient;
     assetManifest = MockAssetManifest();
+    mockHttpClient = MockHttpClient();
+    GoogleFonts.config.httpClient = mockHttpClient;
     GoogleFonts.config.allowRuntimeFetching = true;
     when(mockHttpClient.gets(any)).thenAnswer((_) async {
       return http.Response(_fakeResponse, 200);