Send combination keysyms for some Japanese keys

Windows doesn't give us stable symbols for a bunch of Japanese IM keys,
instead alternating between two symbols. This state is not synchronised
with the IM running on the remote server so to have stable behaviour we
have to collapse these multiple symbols in to a single keysym.

core/input/util.js

@@ -157,6 +157,21 @@ export function getKeysym(evt) {
             }
         }
 
+        // Windows sends alternating symbols for some keys when using a
+        // Japanese layout. We have no way of synchronising with the IM
+        // running on the remote system, so we send some combined keysym
+        // instead and hope for the best.
+        if (browser.isWindows()) {
+            switch (key) {
+                case 'Zenkaku':
+                case 'Hankaku':
+                    return KeyTable.XK_Zenkaku_Hankaku;
+                case 'Romaji':
+                case 'KanaMode':
+                    return KeyTable.XK_Romaji;
+            }
+        }
+
         return DOMKeyTable[key][location];
     }
 

tests/test.helper.js

@@ -186,5 +186,38 @@ describe('Helpers', function () {
                 expect(KeyboardUtil.getKeysym({code: 'NumpadDecimal', key: ',', location: 3})).to.be.equal(0xFFAC);
             });
         });
+
+        describe('Japanese IM keys on Windows', function () {
+            let origNavigator;
+            beforeEach(function () {
+                // window.navigator is a protected read-only property in many
+                // environments, so we need to redefine it whilst running these
+                // tests.
+                origNavigator = Object.getOwnPropertyDescriptor(window, "navigator");
+
+                Object.defineProperty(window, "navigator", {value: {}});
+                if (window.navigator.platform !== undefined) {
+                    // Object.defineProperty() doesn't work properly in old
+                    // versions of Chrome
+                    this.skip();
+                }
+
+                window.navigator.platform = "Windows";
+            });
+
+            afterEach(function () {
+                if (origNavigator !== undefined) {
+                    Object.defineProperty(window, "navigator", origNavigator);
+                }
+            });
+
+            const keys = { 'Zenkaku': 0xff2a, 'Hankaku': 0xff2a,
+                           'Romaji': 0xff24, 'KanaMode': 0xff24 };
+            for (let [key, keysym] of Object.entries(keys)) {
+                it(`should fake combined key for ${key} on Windows`, function () {
+                    expect(KeyboardUtil.getKeysym({code: 'FakeIM', key: key})).to.be.equal(keysym);
+                });
+            }
+        });
     });
 });