Add overloads for lookup that lets you specify a bundle (#8007)

* Add overloads for lookup that lets you specify a bundle

* check bundle with defaultBundleIdentifier before main bundle

shell/platform/darwin/ios/framework/Headers/FlutterDartProject.h

@@ -26,14 +26,26 @@ FLUTTER_EXPORT
 - (instancetype)initFromDefaultSourceForConfiguration FLUTTER_UNAVAILABLE("Use -init instead.");
 
 /**
- * Returns the file name for the given asset.
- * The returned file name can be used to access the asset in the application's main bundle.
+ * Returns the file name for the given asset. If the bundle with the identifier
+ * "io.flutter.flutter.app" exists, it will try use that bundle; otherwise, it
+ * will use the main bundle.  To specify a different bundle, use
+ * `-lookupKeyForAsset:asset:fromBundle`.
  *
  * @param asset The name of the asset. The name can be hierarchical.
  * @return the file name to be used for lookup in the main bundle.
  */
 + (NSString*)lookupKeyForAsset:(NSString*)asset;
 
+/**
+ * Returns the file name for the given asset.
+ * The returned file name can be used to access the asset in the supplied bundle.
+ *
+ * @param asset The name of the asset. The name can be hierarchical.
+ * @param bundle The `NSBundle` to use for looking up the asset.
+ * @return the file name to be used for lookup in the main bundle.
+ */
++ (NSString*)lookupKeyForAsset:(NSString*)asset fromBundle:(NSBundle*)bundle;
+
 /**
  * Returns the file name for the given asset which originates from the specified package.
  * The returned file name can be used to access the asset in the application's main bundle.
@@ -44,6 +56,19 @@ FLUTTER_EXPORT
  */
 + (NSString*)lookupKeyForAsset:(NSString*)asset fromPackage:(NSString*)package;
 
+/**
+ * Returns the file name for the given asset which originates from the specified package.
+ * The returned file name can be used to access the asset in the specified bundle.
+ *
+ * @param asset The name of the asset. The name can be hierarchical.
+ * @param package The name of the package from which the asset originates.
+ * @param bundle The bundle to use when doing the lookup.
+ * @return the file name to be used for lookup in the main bundle.
+ */
++ (NSString*)lookupKeyForAsset:(NSString*)asset
+                   fromPackage:(NSString*)package
+                    fromBundle:(NSBundle*)bundle;
+
 /**
  * Returns the default identifier for the bundle where we expect to find the Flutter Dart
  * application.

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -199,6 +199,12 @@ static blink::Settings DefaultSettingsForProcess(NSBundle* bundle = nil) {
 #pragma mark - Assets-related utilities
 
 + (NSString*)flutterAssetsName:(NSBundle*)bundle {
+  if (bundle == nil) {
+    bundle = [NSBundle bundleWithIdentifier:[FlutterDartProject defaultBundleIdentifier]];
+  }
+  if (bundle == nil) {
+    bundle = [NSBundle mainBundle];
+  }
   NSString* flutterAssetsName = [bundle objectForInfoDictionaryKey:@"FLTAssetsPath"];
   if (flutterAssetsName == nil) {
     flutterAssetsName = @"Frameworks/App.framework/flutter_assets";
@@ -207,12 +213,23 @@ static blink::Settings DefaultSettingsForProcess(NSBundle* bundle = nil) {
 }
 
 + (NSString*)lookupKeyForAsset:(NSString*)asset {
-  NSString* flutterAssetsName = [FlutterDartProject flutterAssetsName:[NSBundle mainBundle]];
+  return [self lookupKeyForAsset:asset fromBundle:nil];
+}
+
++ (NSString*)lookupKeyForAsset:(NSString*)asset fromBundle:(NSBundle*)bundle {
+  NSString* flutterAssetsName = [FlutterDartProject flutterAssetsName:bundle];
   return [NSString stringWithFormat:@"%@/%@", flutterAssetsName, asset];
 }
 
 + (NSString*)lookupKeyForAsset:(NSString*)asset fromPackage:(NSString*)package {
-  return [self lookupKeyForAsset:[NSString stringWithFormat:@"packages/%@/%@", package, asset]];
+  return [self lookupKeyForAsset:asset fromPackage:package fromBundle:nil];
+}
+
++ (NSString*)lookupKeyForAsset:(NSString*)asset
+                   fromPackage:(NSString*)package
+                    fromBundle:(NSBundle*)bundle {
+  return [self lookupKeyForAsset:[NSString stringWithFormat:@"packages/%@/%@", package, asset]
+                      fromBundle:bundle];
 }
 
 + (NSString*)defaultBundleIdentifier {