Implement hasStrings in terms of getClipboardData on Android

Author: justinmc

shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformChannel.java

@@ -155,6 +155,14 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result
                   result.success(null);
                   break;
                 }
+              case "Clipboard.hasStrings":
+                {
+                  boolean hasStrings = platformMessageHandler.clipboardHasStrings();
+                  JSONObject response = new JSONObject();
+                  response.put("value", hasStrings);
+                  result.success(response);
+                  break;
+                }
               default:
                 result.notImplemented();
                 break;
@@ -426,6 +434,11 @@ public interface PlatformMessageHandler {
      * {@code text}.
      */
     void setClipboardData(@NonNull String text);
+
+    /** The Flutter application would like to know if the clipboard currently contains a string
+     *  that can be pasted.
+     */
+    boolean clipboardHasStrings();
   }
 
   /** Types of sounds the Android OS can play on behalf of an application. */

shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java

@@ -85,6 +85,12 @@ public CharSequence getClipboardData(
         public void setClipboardData(@NonNull String text) {
           PlatformPlugin.this.setClipboardData(text);
         }
+
+        @Override
+        public boolean clipboardHasStrings() {
+          CharSequence data = PlatformPlugin.this.getClipboardData(PlatformChannel.ClipboardContentFormat.PLAIN_TEXT);
+          return data != null && data.length() > 0;
+        }
       };
 
   public PlatformPlugin(Activity activity, PlatformChannel platformChannel) {