MacViews: Implement InputMethodMac::CancelComposition.

ui/base/ime/BUILD.gn

 # Copyright 2015 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 source_set("text_input_types") {
   sources = [
     "text_input_flags.h",
@@ skipping 176 matching lines @@
     deps += [ "//ui/gfx/x" ]
   }
 
   if (is_win) {
     cflags = [ "/wd4324" ]  # Structure was padded due to __declspec(align()), which is
                             # uninteresting.
 
     libs = [ "imm32.lib" ]
   }
 
+  if (is_mac) {
+    libs = [ "AppKit.framework" ]
+  }
+
   if (use_ozone) {
     deps += [
       "//ui/events/ozone:events_ozone_layout",
       "//ui/ozone",
     ]
   }
 }