Adds a test for setting empty composition text.

chrome/test/data/extensions/api_test/input_ime_nonchromeos/background.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var failToSendKeyEvents = 'Could not send key events';
 
 chrome.test.runTests([
   // Tests input.ime.activate and input.ime.onFocus APIs.
   function testActivateAndFocus() {
     var focused = false;
@@ skipping 65 matching lines @@
       text: 'test_set_composition',
       cursor: 2
     }, function() {
       if(chrome.runtime.lastError) {
         chrome.test.fail();
         return;
       }
       chrome.test.succeed();
     });
   },
+  function testEmptyComposition() {
+    chrome.input.ime.setComposition({
+      contextID: 1,
+      text: '',
+      cursor: 0
+    }, function() {
+      if(chrome.runtime.lastError) {
+        chrome.test.fail();
+        return;
+      }
+      chrome.test.succeed();
+    });
+  },
   // Test input.ime.sendKeyEvents API.
   function testSendKeyEvents() {
     // Sends a normal character key.
     chrome.input.ime.sendKeyEvents({
       contextID: 1,
       keyData: [{
         type: 'keydown',
         requestId: '0',
         key: 'a',
         code: 'KeyA'
@@ skipping 52 matching lines @@
       if (context.type != 'none') {
         // Waits for the 'get_blur_event' message in
         // InputImeApiTest.BasicApiTest.
         chrome.test.sendMessage('get_blur_event');
       }
       chrome.test.succeed();
     });
     chrome.test.succeed();
   }
 ]);