Only enable improved SafeBrowsing download protection on Windows.

chrome/browser/safe_browsing/download_protection_service.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/safe_browsing/download_protection_service.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 509 matching lines @@
       // binaries whose certificate match the whitelist.
       reason = REASON_TRUSTED_EXECUTABLE;
     }
     if (reason != REASON_MAX) {
       RecordImprovedProtectionStats(reason);
       CheckDigestList();
     } else if (!pingback_enabled_) {
       RecordImprovedProtectionStats(REASON_PING_DISABLED);
       CheckDigestList();
     } else {
+      // Currently, the UI only works on Windows so we don't even bother
+      // with pinging the server if we're not on Windows.  TODO(noelutz):
+      // change this code once the UI is done for Linux and Mac.
+#if defined(OS_WIN)
       // The URLFetcher is owned by the UI thread, so post a message to
       // start the pingback.
       BrowserThread::PostTask(
           BrowserThread::UI,
           FROM_HERE,
           base::Bind(&CheckClientDownloadRequest::SendRequest, this));
+#else
+      RecordImprovedProtectionStats(REASON_OS_NOT_SUPPORTED);
+      CheckDigestList();
+#endif
     }
   }
 
   void SendRequest() {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
     // This is our last chance to check whether the request has been canceled
     // before sending it.
     if (!service_) {
       RecordImprovedProtectionStats(REASON_REQUEST_CANCELED);
@@ skipping 152 matching lines @@
 
 void DownloadProtectionService::RequestFinished(
     CheckClientDownloadRequest* request) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   std::set<scoped_refptr<CheckClientDownloadRequest> >::iterator it =
       download_requests_.find(request);
   DCHECK(it != download_requests_.end());
   download_requests_.erase(*it);
 }
 }  // namespace safe_browsing