Let injectPlugins integrate custom pods (#26970)

diff --git a/packages/flutter_tools/lib/src/ios/cocoapods.dart b/packages/flutter_tools/lib/src/ios/cocoapods.dart
index 92b7a3e..7686ef8 100644
--- a/packages/flutter_tools/lib/src/ios/cocoapods.dart
+++ b/packages/flutter_tools/lib/src/ios/cocoapods.dart

@@ -193,6 +193,12 @@
       ));
       podfileTemplate.copySync(podfile.path);
     }
+    addPodsDependencyToFlutterXcconfig(iosProject);
+  }
+
+  /// Ensures all `Flutter/Xxx.xcconfig` files for the given iOS sub-project of
+  /// a parent Flutter project include pods configuration.
+  void addPodsDependencyToFlutterXcconfig(IosProject iosProject) {
     _addPodsDependencyToFlutterXcconfig(iosProject, 'Debug');
     _addPodsDependencyToFlutterXcconfig(iosProject, 'Release');
   }

diff --git a/packages/flutter_tools/lib/src/plugins.dart b/packages/flutter_tools/lib/src/plugins.dart
index cd4827b..5f67181 100644
--- a/packages/flutter_tools/lib/src/plugins.dart
+++ b/packages/flutter_tools/lib/src/plugins.dart

@@ -298,9 +298,16 @@
   await _writeAndroidPluginRegistrant(project, plugins);
   await _writeIOSPluginRegistrant(project, plugins);
   if (!project.isModule && project.ios.hostAppRoot.existsSync()) {
+    final IosProject iosProject = IosProject.fromFlutter(project);
     final CocoaPods cocoaPods = CocoaPods();
-    if (plugins.isNotEmpty)
+    if (plugins.isNotEmpty) {
       cocoaPods.setupPodfile(project.ios);
+    }
+    /// The user may have a custom maintained Podfile that they're running `pod install`
+    /// on themselves.
+    else if (iosProject.podfile.existsSync() && iosProject.podfileLock.existsSync()) {
+      cocoaPods.addPodsDependencyToFlutterXcconfig(iosProject);
+    }
   }
 }
 

diff --git a/packages/flutter_tools/lib/src/project.dart b/packages/flutter_tools/lib/src/project.dart
index 4c5496b..9e4bdac 100644
--- a/packages/flutter_tools/lib/src/project.dart
+++ b/packages/flutter_tools/lib/src/project.dart

@@ -89,7 +89,7 @@
   }
 
   /// The iOS sub project of this project.
-  IosProject get ios => IosProject._(this);
+  IosProject get ios => IosProject.fromFlutter(this);
 
   /// The Android sub project of this project.
   AndroidProject get android => AndroidProject._(this);
@@ -151,7 +151,7 @@
 /// Instances will reflect the contents of the `ios/` sub-folder of
 /// Flutter applications and the `.ios/` sub-folder of Flutter module projects.
 class IosProject {
-  IosProject._(this.parent);
+  IosProject.fromFlutter(this.parent);
 
   /// The parent of this project.
   final FlutterProject parent;