Make URLRequestContextBuilder use base/task_scheduler/

net/url_request/url_request_context_builder.h

Index: net/url_request/url_request_context_builder.h
diff --git a/net/url_request/url_request_context_builder.h b/net/url_request/url_request_context_builder.h
index 2a520017cae85457ef517e3a0daf942eba8e52dc..e4c77c66aa896fd69d75db0705cf7ac559ca2d81 100644
--- a/net/url_request/url_request_context_builder.h
+++ b/net/url_request/url_request_context_builder.h
@@ -26,6 +26,7 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/task_scheduler/task_traits.h"
 #include "build/build_config.h"
 #include "net/base/net_export.h"
 #include "net/base/network_delegate.h"
@@ -42,6 +43,8 @@
 
 namespace base {
 class SingleThreadTaskRunner;
+class SequencedTaskRunner;
+class TaskRunner;
 }
 
 namespace net {
@@ -325,8 +328,8 @@ class NET_EXPORT URLRequestContextBuilder {
       std::unique_ptr<CookieStore> cookie_store,
       std::unique_ptr<ChannelIDService> channel_id_service);
 
-  // Sets the task runner used to perform file operations. If not set, one will
-  // be created.
+  // Sets the task runner used to perform file operations. If not set,
+  // TaskSchedulers will be used instead.
   void SetFileTaskRunner(
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
 
@@ -358,6 +361,16 @@ class NET_EXPORT URLRequestContextBuilder {
       NetworkDelegate* network_delegate,
       NetLog* net_log);
 
+  // Returns a TaskRunner with the specified traits. If |file_task_runner_| is
+  // non-NULL, uses that. Otherwise, uses base/task_scheduler/ and the specified
+  // traits.

[Randy Smith (Not in Mondays), 2017/06/27 21:00:51]

Confirming that it's intentional on your part that these are above the 'private'
line, and hence that you have a use case in mind for subclasses using them?

(If you haven't already queued the CL up, my personal preference would be that
these be private methods and they be shifted out to protected when first used. 
But I'm ok with this if you prefer it.)

[mmenke, 2017/06/27 21:10:25]

Yes, that's deliberate.  While I'm not sure subclasses ever will need them, it
seems reasonable for them to have access.  I generally prefer to err on the side
of making things private, but in this case, these just seemed very reasonable to
expose from the start.

+  scoped_refptr<base::TaskRunner> GetFileTaskRunner(
+      const base::TaskTraits& traits);
+  scoped_refptr<base::SequencedTaskRunner> GetFileSequencedTaskRunner(
+      const base::TaskTraits& traits);
+  scoped_refptr<base::SingleThreadTaskRunner> GetFileSingleThreadTaskRunner(
+      const base::TaskTraits& traits);

[Randy Smith (Not in Mondays), 2017/06/27 21:00:51]

Thought (i.e. a notch underneath suggestion): At this point, each of these
routines is only called once, which seems like not much work for the overhead of
three additions to the interface.  If you hoisted the calls into their calling
locations, I think it would be fewer total LOC.  Alternatively, combining the
three calls might work (though that would seem to require an enum, which is
ugly).  Anyway, just raising the question as to whether there are other ways you
want to structure this.

[mmenke, 2017/06/27 21:10:25]

I'll have to use these again for the cookie store (and presumably the channel ID
store), at least, so while they are called only once, I think this is simplest
for future changes.

Also, I can't merge them, unless I use a template - they each return different
types.

Once most things are hooked up, I'm thinking I'll eventually do a simplification
pass over this class, figure out what's needed, what's not.

+
  private:
   const char* name_;
   bool enable_brotli_;