Make SpellCheckPanel compiled and used only on Mac

components/spellcheck/renderer/BUILD.gn

Index: components/spellcheck/renderer/BUILD.gn
diff --git a/components/spellcheck/renderer/BUILD.gn b/components/spellcheck/renderer/BUILD.gn
index 1c3e482f24d6aebd5812c59a954c67be0a608e00..e962635925fb4788efe1306869ff0e2dcc3d7a04 100644
--- a/components/spellcheck/renderer/BUILD.gn
+++ b/components/spellcheck/renderer/BUILD.gn
@@ -25,6 +25,7 @@ source_set("renderer") {
     "spelling_engine.h",
   ]
 
+  #TODO(xiaochengh): Negate these checks so that each file is listed only once.

[Lei Zhang, 2017/04/14 01:24:39]

nit: space after '#'

[Xiaocheng, 2017/04/14 01:29:59]

Whoops. Done.

   if (!use_browser_spellchecker) {
     sources -= [
       "platform_spelling_engine.cc",
@@ -32,6 +33,13 @@ source_set("renderer") {
     ]
   }
 
+  if (!has_spellcheck_panel) {
+    sources -= [
+      "spellcheck_panel.cc",
+      "spellcheck_panel.h",
+    ]
+  }
+
   if (is_android) {
     sources -= [
       "hunspell_engine.cc",