Update Mac plugin IME handling to match updated spec

third_party/mozilla/ComplexTextInputPanel.mm

Index: third_party/mozilla/ComplexTextInputPanel.mm
diff --git a/third_party/mozilla/ComplexTextInputPanel.mm b/third_party/mozilla/ComplexTextInputPanel.mm
index 638ed9df3534d373a53ba1edbdc6a881090134dc..0eb49e2d6a1493e458ced4042cd67dbf61d9534f 100644
--- a/third_party/mozilla/ComplexTextInputPanel.mm
+++ b/third_party/mozilla/ComplexTextInputPanel.mm
@@ -98,8 +98,7 @@ static NSString* const NSTextInputContextKeyboardSelectionDidChangeNotification
 
 - (void)keyboardInputSourceChanged:(NSNotification *)notification
 {
-  [mInputTextView setString:@""];
-  [self orderOut:nil];
+  [self cancelComposition];
 }
 
 - (BOOL)interpretKeyEvent:(NSEvent*)event string:(NSString**)string
@@ -129,15 +128,20 @@ static NSString* const NSTextInputContextKeyboardSelectionDidChangeNotification
   return hadMarkedText;
 }
 
-- (void)cancelInput
+- (NSTextInputContext*)inputContext
+{
+  return [mInputTextView inputContext];
+}
+
+- (void)cancelComposition
 {
-  [self orderOut:nil];
   [mInputTextView setString:@""];
+  [self orderOut:nil];
 }
 
-- (NSTextInputContext*)inputContext
+- (BOOL)inComposition
 {
-  return [mInputTextView inputContext];
+  return [mInputTextView hasMarkedText];
 }
 
 @end