[webview_flutter] Fix wrong main thread checking condition. (#1602) The Android JavaScriptChannel wasn't checking correctly if messages are received on the main thread and took the branch that assumes we are on the main thread. https://github.com/flutter/engine/pull/8830 causes this behavior to fail (which is good). So now we can also add an e2e test that fails with the buggy behavior.

diff --git a/packages/webview_flutter/CHANGELOG.md b/packages/webview_flutter/CHANGELOG.md
index 973073a..19a0fcd 100644
--- a/packages/webview_flutter/CHANGELOG.md
+++ b/packages/webview_flutter/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.7+1
+
+* Fix an issue where JavaScriptChannel messages weren't sent from the platform thread on Android.
+
 ## 0.3.7
 
 * Fix loadUrlWithHeaders flaky test.

diff --git a/packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/JavaScriptChannel.java b/packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/JavaScriptChannel.java
index 180ca4f..f23aae5 100644
--- a/packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/JavaScriptChannel.java
+++ b/packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/JavaScriptChannel.java

@@ -49,7 +49,7 @@
             methodChannel.invokeMethod("javascriptChannelMessage", arguments);
           }
         };
-    if (platformThreadHandler.getLooper() == Looper.getMainLooper()) {
+    if (platformThreadHandler.getLooper() == Looper.myLooper()) {
       postMessageRunnable.run();
     } else {
       platformThreadHandler.post(postMessageRunnable);

diff --git a/packages/webview_flutter/example/test_driver/webview.dart b/packages/webview_flutter/example/test_driver/webview.dart
index 09b4f39..7a290a0 100644
--- a/packages/webview_flutter/example/test_driver/webview.dart
+++ b/packages/webview_flutter/example/test_driver/webview.dart

@@ -91,6 +91,47 @@
         .evaluateJavascript('document.documentElement.innerText');
     expect(content.contains('flutter_test_header'), isTrue);
   });
+
+  test('JavaScriptChannel', () async {
+    final Completer<WebViewController> controllerCompleter =
+        Completer<WebViewController>();
+    final Completer<void> pageLoaded = Completer<void>();
+    final List<String> messagesReceived = <String>[];
+    await pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: WebView(
+          key: GlobalKey(),
+          // This is the data URL for: '<!DOCTYPE html>'
+          initialUrl:
+              'data:text/html;charset=utf-8;base64,PCFET0NUWVBFIGh0bWw+',
+          onWebViewCreated: (WebViewController controller) {
+            controllerCompleter.complete(controller);
+          },
+          javascriptMode: JavascriptMode.unrestricted,
+          // TODO(iskakaushik): Remove this when collection literals makes it to stable.
+          // ignore: prefer_collection_literals
+          javascriptChannels: <JavascriptChannel>[
+            JavascriptChannel(
+              name: 'Echo',
+              onMessageReceived: (JavascriptMessage message) {
+                messagesReceived.add(message.message);
+              },
+            ),
+          ].toSet(),
+          onPageFinished: (String url) {
+            pageLoaded.complete(null);
+          },
+        ),
+      ),
+    );
+    final WebViewController controller = await controllerCompleter.future;
+    await pageLoaded.future;
+
+    expect(messagesReceived, isEmpty);
+    await controller.evaluateJavascript('Echo.postMessage("hello");');
+    expect(messagesReceived, equals(<String>['hello']));
+  });
 }
 
 Future<void> pumpWidget(Widget widget) {

diff --git a/packages/webview_flutter/pubspec.yaml b/packages/webview_flutter/pubspec.yaml
index 7ea66ca..789657a 100644
--- a/packages/webview_flutter/pubspec.yaml
+++ b/packages/webview_flutter/pubspec.yaml

@@ -1,6 +1,6 @@
 name: webview_flutter
 description: A Flutter plugin that provides a WebView widget on Android and iOS.
-version: 0.3.7
+version: 0.3.7+1
 author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/webview_flutter