Enable Windows platform_channel test (#106973)

.ci.yaml

@@ -3994,7 +3994,6 @@ targets:
         ["devicelab", "hostonly"]
       task_name: platform_channel_sample_test_windows
     scheduler: luci
-    bringup: true
 
   - name: Windows plugin_dependencies_test
     recipe: devicelab/devicelab_drone

examples/platform_channel/lib/main.dart

@@ -28,9 +28,13 @@ class _PlatformChannelState extends State<PlatformChannel> {
     try {
       final int? result = await methodChannel.invokeMethod('getBatteryLevel');
       batteryLevel = 'Battery level: $result%.';
-    } on PlatformException {
+    } on PlatformException catch (e) {
+      if (e.code == 'NO_BATTERY') {
+        batteryLevel = 'No battery.';
+      } else {
         batteryLevel = 'Failed to get battery level.';
       }
+    }
     setState(() {
       _batteryLevel = batteryLevel;
     });

examples/platform_channel/test_driver/button_tap_test.dart

@@ -31,7 +31,11 @@ void main() {
         batteryLevel = await driver.getText(batteryLevelLabel);
       }
 
-      expect(batteryLevel.contains('%'), isTrue);
+      // Allow either a battery percentage or "No battery" since it will vary
+      // by device; either indicates that a known response came from the host
+      // implementation.
+      expect(batteryLevel.contains('%') || batteryLevel.contains('No battery'),
+          isTrue);
     });
   });
 }

examples/platform_channel/windows/runner/flutter_window.cpp

@@ -16,10 +16,17 @@
 
 #include "flutter/generated_plugin_registrant.h"
 
+static constexpr int kBatteryError = -1;
+static constexpr int kNoBattery = -2;
+
 static int GetBatteryLevel() {
   SYSTEM_POWER_STATUS status;
-  if (GetSystemPowerStatus(&status) == 0 || status.BatteryLifePercent == 255) {
-    return -1;
+  if (GetSystemPowerStatus(&status) == 0) {
+    return kBatteryError;
+  } else if (status.BatteryFlag == 128) {
+    return kNoBattery;
+  } else if (status.BatteryLifePercent == 255) {
+    return kBatteryError;
   }
   return status.BatteryLifePercent;
 }
@@ -59,10 +66,12 @@ bool FlutterWindow::OnCreate() {
         if (call.method_name() == "getBatteryLevel") {
           int battery_level = GetBatteryLevel();
 
-          if (battery_level != -1) {
-            result->Success(battery_level);
-          } else {
+          if (battery_level == kBatteryError) {
             result->Error("UNAVAILABLE", "Battery level not available.");
+          } else if (battery_level == kNoBattery) {
+            result->Error("NO_BATTERY", "Device does not have a battery.");
+          } else {
+            result->Success(battery_level);
           }
         } else {
           result->NotImplemented();