Use ResourceRequestInfo::GetWebContents in DownloadRequestLimiter

chrome/browser/download/download_request_limiter.h

Index: chrome/browser/download/download_request_limiter.h
diff --git a/chrome/browser/download/download_request_limiter.h b/chrome/browser/download/download_request_limiter.h
index 50ea982aa3adc519927d826ed870d3fdb405391b..7c7d1e57c088fc23c6481837af3656975d72a0cc 100644
--- a/chrome/browser/download/download_request_limiter.h
+++ b/chrome/browser/download/download_request_limiter.h
@@ -182,11 +182,11 @@ class DownloadRequestLimiter
   DownloadStatus GetDownloadStatus(content::WebContents* tab);
 
   // Check if download can proceed and notifies the callback on UI thread.
-  void CanDownload(int render_process_host_id,
-                   int render_view_id,
-                   const GURL& url,
-                   const std::string& request_method,
-                   const Callback& callback);
+  void CanDownload(
+      const base::Callback<content::WebContents*(void)>& web_contents_getter,

[asanka, 2015/11/24 16:13:19]

Instead of a bunch of naked base::Callback<>s, could you define a type somewhere
and use it here? That way you can describe what the callback does and its
guarantees. A naked callback doesn't imply anything about thread restrictions,
lifetime guarantees, validity etc.. (E.g. a callback that's bound to a method on
an object referenced via a weak pointer will become null when the weak reference
is invalidated. It's not sufficient that the callback be bound. For a callback
to be valid, the weak reference to the object against which the method call is
indirected must also be valid).

Everywhere you use the callback, you are assume that it's non-null with no API
contract anywhere that it is.

[clamy, 2015/11/25 14:02:02]

I went back to having a typedef in ResourceRequestInfo, with additional
precision about the callback.

+      const GURL& url,
+      const std::string& request_method,
+      const Callback& callback);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(DownloadTest, DownloadResourceThrottleCancels);
@@ -215,11 +215,11 @@ class DownloadRequestLimiter
                        const Callback& callback);
 
   // Invoked when decision to download has been made.
-  void OnCanDownloadDecided(int render_process_host_id,
-                            int render_view_id,
-                            const std::string& request_method,
-                            const Callback& orig_callback,
-                            bool allow);
+  void OnCanDownloadDecided(
+      const base::Callback<content::WebContents*(void)>& web_contents_getter,
+      const std::string& request_method,
+      const Callback& orig_callback,
+      bool allow);
 
   // Removes the specified TabDownloadState from the internal map and deletes
   // it. This has the effect of resetting the status for the tab to