[benchmarks] disable partial repaint for multiple backdrop blur iOS macrobenchmarks. (#137902)

Partial repaint is too effective, and we'd like to be able to measure performance without carefully structuring the benchmarks. For example, right now partial repaint is culling any blurs in the multibackdrop case, which we should be using to track  https://github.com/flutter/flutter/issues/132735

dev/devicelab/lib/tasks/perf_tests.dart

@@ -143,6 +143,7 @@ TaskFunction createBackdropFilterPerfTest({
     testDriver: 'test_driver/backdrop_filter_perf_test.dart',
     saveTraceFile: true,
     enableImpeller: enableImpeller,
+    disablePartialRepaint: true,
   ).run;
 }
 
@@ -767,6 +768,51 @@ Map<String, dynamic> _average(List<Map<String, dynamic>> results, int iterations
   return tally;
 }
 
+/// Opens the file at testDirectory + 'ios/Runner/Info.plist'
+/// and adds the following entry to the application.
+/// <FTLDisablePartialRepaint/>
+/// <true/>
+void _disablePartialRepaint(String testDirectory) {
+  final String manifestPath = path.join(
+      testDirectory, 'ios', 'Runner', 'Info.plist');
+  final File file = File(manifestPath);
+
+  if (!file.existsSync()) {
+    throw Exception('Info.plist not found at $manifestPath');
+  }
+
+  final String xmlStr = file.readAsStringSync();
+  final XmlDocument xmlDoc = XmlDocument.parse(xmlStr);
+  final List<(String, String)> keyPairs = <(String, String)>[
+    ('FLTDisablePartialRepaint', 'true'),
+  ];
+
+  final XmlElement applicationNode =
+      xmlDoc.findAllElements('dict').first;
+
+  // Check if the meta-data node already exists.
+  for (final (String key, String value) in keyPairs) {
+    applicationNode.children.add(XmlElement(XmlName('key'), <XmlAttribute>[], <XmlNode>[
+      XmlText(key)
+    ], false));
+    applicationNode.children.add(XmlElement(XmlName(value)));
+  }
+
+  file.writeAsStringSync(xmlDoc.toXmlString(pretty: true, indent: '    '));
+}
+
+Future<void> _resetPlist(String testDirectory) async {
+  final String manifestPath = path.join(
+      testDirectory, 'ios', 'Runner', 'Info.plist');
+  final File file = File(manifestPath);
+
+  if (!file.existsSync()) {
+    throw Exception('Info.plist not found at $manifestPath');
+  }
+
+  await exec('git', <String>['checkout', file.path]);
+}
+
 /// Opens the file at testDirectory + 'android/app/src/main/AndroidManifest.xml'
 /// and adds the following entry to the application.
 /// <meta-data
@@ -1124,6 +1170,7 @@ class PerfTest {
     this.timeoutSeconds,
     this.enableImpeller,
     this.forceOpenGLES,
+    this.disablePartialRepaint = false,
   }): _resultFilename = resultFilename;
 
   const PerfTest.e2e(
@@ -1142,6 +1189,7 @@ class PerfTest {
     this.timeoutSeconds,
     this.enableImpeller,
     this.forceOpenGLES,
+    this.disablePartialRepaint = false,
   }) : saveTraceFile = false, timelineFileName = null, _resultFilename = resultFilename;
 
   /// The directory where the app under test is defined.
@@ -1181,6 +1229,9 @@ class PerfTest {
   /// Whether the perf test force Impeller's OpenGLES backend.
   final bool? forceOpenGLES;
 
+  /// Whether partial repaint functionality should be disabled (iOS only).
+  final bool disablePartialRepaint;
+
   /// Number of seconds to time out the test after, allowing debug callbacks to run.
   final int? timeoutSeconds;
 
@@ -1230,14 +1281,42 @@ class PerfTest {
       final String? localEngineHost = localEngineHostFromEnv;
       final String? localEngineSrcPath = localEngineSrcPathFromEnv;
 
-      Future<void> Function()? manifestReset;
-      if (forceOpenGLES ?? false) {
-        assert(enableImpeller!);
-        _addOpenGLESToManifest(testDirectory);
-        manifestReset = () => _resetManifest(testDirectory);
+      bool changedPlist = false;
+      bool changedManifest = false;
+
+      Future<void> resetManifest() async {
+        if (!changedManifest) {
+          return;
+        }
+        try {
+          await _resetManifest(testDirectory);
+        } catch (err) {
+          print('Caught exception while trying to reset AndroidManifest: $err');
+        }
+      }
+
+      Future<void> resetPlist() async {
+        if (!changedPlist) {
+          return;
+        }
+        try {
+          await _resetPlist(testDirectory);
+        } catch (err) {
+           print('Caught exception while trying to reset Info.plist: $err');
+        }
       }
 
       try {
+        if (forceOpenGLES ?? false) {
+          assert(enableImpeller!);
+          changedManifest = true;
+          _addOpenGLESToManifest(testDirectory);
+        }
+        if (disablePartialRepaint) {
+          changedPlist = true;
+          _disablePartialRepaint(testDirectory);
+        }
+
         final List<String> options = <String>[
           if (localEngine != null) ...<String>['--local-engine', localEngine],
           if (localEngineHost != null) ...<String>[
@@ -1278,9 +1357,8 @@ class PerfTest {
           await flutter('drive', options: options);
         }
       } finally {
-        if (manifestReset != null) {
-          await manifestReset();
-        }
+        await resetManifest();
+        await resetPlist();
       }
 
       final Map<String, dynamic> data = json.decode(