Offload disk accesses to WorkerPool in ExtensionProtocolHandler

net/url_request/url_request_simple_job.h

Index: net/url_request/url_request_simple_job.h
===================================================================
--- net/url_request/url_request_simple_job.h	(revision 145483)
+++ net/url_request/url_request_simple_job.h	(working copy)
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/memory/weak_ptr.h"
+#include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 #include "net/url_request/url_request_job.h"
 
@@ -30,15 +31,24 @@
  protected:
   virtual ~URLRequestSimpleJob();
 
-  // subclasses must override the way response data is determined.
-  virtual bool GetData(std::string* mime_type,
-                       std::string* charset,
-                       std::string* data) const = 0;
+  // Subclasses must override the way response data is determined.
+  // The return value should be net::OK if data is obtained;
+  // net::ERR_IO_PENDING if processing in another thread is needed to finish
+  // obtaining data; and net::ERR_FAILED to indicate an error. If method
+  // returns net::ERR_IO_PENDING then |callback| should be called when
+  // operation is completed. In other situations |callback| should never be
+  // called.

[wtc, 2012/07/11 01:08:46]

Nit: remove net:: in this comment block because this class
is inside the net namespace.

should be called => will be called
should never be called => will not be called

[wtc, 2012/07/11 18:48:50]

I see.  Then the use of "should" is appropriate in this comment.
Sorry about my confusion.

Nit: the second sentence might be clearer in a bullet point
form:

  The return value should be
  * OK if data is obtained;
  * ERR_IO_PENDING if processing in another thread is needed to finish obtaining
data; and
  * ERR_FAILED to indicate an error.

+  virtual int GetData(std::string* mime_type,
+                      std::string* charset,
+                      std::string* data,
+                      const CompletionCallback& callback) const = 0;
 
  protected:
   void StartAsync();
 
  private:
+  void OnGetDataCompleted(int result);
+
   std::string mime_type_;
   std::string charset_;
   std::string data_;