Collect some histograms about signed binary downloads.

chrome/browser/safe_browsing/safe_browsing_service.cc

Index: chrome/browser/safe_browsing/safe_browsing_service.cc
===================================================================
--- chrome/browser/safe_browsing/safe_browsing_service.cc	(revision 106761)
+++ chrome/browser/safe_browsing/safe_browsing_service.cc	(working copy)
@@ -175,16 +175,15 @@
         safe_browsing::ClientSideDetectionService::Create(
             g_browser_process->system_request_context()));
   }
-  if (CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableImprovedDownloadProtection)) {
-    download_service_ = new safe_browsing::DownloadProtectionService(
-        this,
-        g_browser_process->system_request_context());
-  }
+  download_service_.reset(new safe_browsing::DownloadProtectionService(
+      this,
+      g_browser_process->system_request_context()));
 #endif
 }
 
 SafeBrowsingService::~SafeBrowsingService() {
+  ShutDownDownloadService();
+
   // Deletes the PrefChangeRegistrars, whose dtors also unregister |this| as an
   // observer of the preferences.
   STLDeleteValues(&prefs_map_);
@@ -216,15 +215,7 @@
 }
 
 void SafeBrowsingService::ShutDown() {
-  if (download_service_.get()) {
-    // Disabling the download service first will ensure that it is
-    // disabled before the SafeBrowsingService object becomes invalid.  The
-    // download service might stay around for a bit since it's
-    // ref-counted but it won't do any harm because it will be
-    // disabled.
-    download_service_->SetEnabled(false);
-    download_service_ = NULL;
-  }
+  ShutDownDownloadService();
   Stop();
   // The IO thread is going away, so make sure the ClientSideDetectionService
   // dtor executes now since it may call the dtor of URLFetcher which relies
@@ -1368,6 +1359,16 @@
 
   if (csd_service_.get())
     csd_service_->SetEnabledAndRefreshState(enable);
-  if (download_service_.get())
-    download_service_->SetEnabled(enable);
+  if (download_service_.get()) {
+    download_service_->SetEnabled(
+        enable && CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableImprovedDownloadProtection));
+  }
 }
+
+void SafeBrowsingService::ShutDownDownloadService() {
+  if (download_service_.get()) {
+    BrowserThread::DeleteSoon(BrowserThread::IO, FROM_HERE,
+                              download_service_.release());
+  }
+}