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

chrome/browser/ui/tab_contents/tab_contents_wrapper.h

Index: chrome/browser/ui/tab_contents/tab_contents_wrapper.h
diff --git a/chrome/browser/ui/tab_contents/tab_contents_wrapper.h b/chrome/browser/ui/tab_contents/tab_contents_wrapper.h
index 3fc5e14ef66cd57737255cc285abaf671cf706b4..7be5b0a932797536c4da08577127c76a6cac2df8 100644
--- a/chrome/browser/ui/tab_contents/tab_contents_wrapper.h
+++ b/chrome/browser/ui/tab_contents/tab_contents_wrapper.h
@@ -22,7 +22,6 @@ class BlockedContentTabHelper;
 class BookmarkTabHelper;
 class ConstrainedWindowTabHelper;
 class CoreTabHelper;
-class DownloadRequestLimiterObserver;
 class ExtensionTabHelper;
 class ExternalProtocolObserver;
 class FaviconTabHelper;
@@ -75,6 +74,19 @@ class SafeBrowsingTabObserver;
 // Wraps WebContents and all of its supporting objects in order to control
 // their ownership and lifetime.
 //
+// WARNING: Not every place where HTML can run has a TabContentsWrapper. This
+// class is *only* used in a visible, actual, tab inside a browser. Examples of
+// things that do not have tab wrappers include:
+// - Extension background pages and popup bubbles
+// - HTML notification bubbles
+// - Screensavers on Chrome OS
+// - Other random places we decide to display HTML over time
+//
+// Consider carefully whether your feature is something that makes sense only
+// when a tab is displayed, or could make sense in other cases we use HTML. It
+// may makes sense to push down into WebContents and make configurable, or at
+// least to make easy for other WebContents hosts to include and support.
+//
 // TODO(avi): Eventually, this class will become TabContents as far as
 // the browser front-end is concerned.
 class TabContentsWrapper : public content::WebContentsObserver {
@@ -268,7 +280,6 @@ class TabContentsWrapper : public content::WebContentsObserver {
   // and silently do their thing live here.)
 
   scoped_ptr<AlternateErrorPageTabObserver> alternate_error_page_tab_observer_;
-  scoped_ptr<DownloadRequestLimiterObserver> download_request_limiter_observer_;
   scoped_ptr<extensions::WebNavigationTabObserver> webnavigation_observer_;
   scoped_ptr<ExternalProtocolObserver> external_protocol_observer_;
   scoped_ptr<OmniboxSearchHint> omnibox_search_hint_;