don't try to call BalloonViewHost on non-cros

Avoids link error:

[14->2/16 ~0] LINK(DLL) initial\chrome.dll
FAILED: python gyp-win-tool link-wrapper "c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\bin\link.exe" /nologo /IMPLIB:initial\chrome.dll.lib /DLL /OUT:initial\chrome.dll /PDB:initial\chrome.dll.pdb @initial\chrome.dll.rsp
browser.balloon_collection_impl_ash.obj : error LNK2019: unresolved external symbol "public: bool __thiscall chromeos::BalloonViewHost::AddWebUIMessageCallback(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class base::Callback<void __cdecl(class base::ListValue const *)> const &)" (?AddWebUIMessageCallback@BalloonViewHost@chromeos@@QAE_NABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@ABV?$Callback@$$A6AXPBVListValue@base@@@Z@base@@@Z) referenced in function
"public: bool __thiscall BalloonCollectionImplAsh::AddWebUIMessageCallback(class Notification const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class base::Callback<void __cdecl(class base::ListValue const *)>
const &)" (?AddWebUIMessageCallback@BalloonCollectionImplAsh@@QAE_NABVNotification@@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@ABV?$Callback@$$A6AXPBVListValue@base@@@Z@base@@@Z)
initial\chrome.dll : fatal error LNK1120: 1 unresolved externals


R=ben@chromium.org,cpu@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10540128

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141789 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/views/ash/balloon_collection_impl_ash.cc

@@ -19,6 +19,7 @@ bool BalloonCollectionImplAsh::AddWebUIMessageCallback(
     const Notification& notification,
     const std::string& message,
     const chromeos::BalloonViewHost::MessageCallback& callback) {
+#if defined(OS_CHROMEOS)
   Balloon* balloon = base().FindBalloon(notification);
   if (!balloon)
     return false;
@@ -29,6 +30,9 @@ bool BalloonCollectionImplAsh::AddWebUIMessageCallback(
   chromeos::BalloonViewHost* balloon_view_host =
       static_cast<chromeos::BalloonViewHost*>(balloon_host);
   return balloon_view_host->AddWebUIMessageCallback(message, callback);
+#else
+  return false;
+#endif
 }
 
 void BalloonCollectionImplAsh::AddSystemNotification(