Fix crashes in DownloadRequestLimiter when extension popups/bubbles initiate downloads automatically

chrome/browser/download/download_request_limiter_observer.cc

Index: chrome/browser/download/download_request_limiter_observer.cc
diff --git a/chrome/browser/download/download_request_limiter_observer.cc b/chrome/browser/download/download_request_limiter_observer.cc
index c5bd6e72293cab5a16a53c13e8f6e5704a699537..60df9ac72b282816eea1c8c569c05b753e178199 100644
--- a/chrome/browser/download/download_request_limiter_observer.cc
+++ b/chrome/browser/download/download_request_limiter_observer.cc
@@ -10,8 +10,10 @@
 using content::WebContents;
 
 DownloadRequestLimiterObserver::DownloadRequestLimiterObserver(
-  WebContents* web_contents)
-    : content::WebContentsObserver(web_contents) {
+  WebContents* web_contents,
+  const DownloadRequestLimiterObserver::DestroyedCallback& on_destroyed)
+    : content::WebContentsObserver(web_contents),
+      on_destroyed_(on_destroyed) {
 }
 
 DownloadRequestLimiterObserver::~DownloadRequestLimiterObserver() {
@@ -22,3 +24,10 @@ void DownloadRequestLimiterObserver::DidGetUserGesture() {
     return;  // NULL in unitests.
   g_browser_process->download_request_limiter()->OnUserGesture(web_contents());
 }
+
+void DownloadRequestLimiterObserver::WebContentsDestroyed(
+    WebContents* contents) {
+  if (!on_destroyed_.is_null())
+    on_destroyed_.Run(this);
+  delete this;
+}