Convert PpdCache and PpdProvider to TaskScheduler.

chromeos/printing/ppd_cache.h

Index: chromeos/printing/ppd_cache.h
diff --git a/chromeos/printing/ppd_cache.h b/chromeos/printing/ppd_cache.h
index ee9ba654cd4abbe6c9814de55d5bfdfa816cefa6..29d974fcff0972269c3572b2d51eed76bbf903df 100644
--- a/chromeos/printing/ppd_cache.h
+++ b/chromeos/printing/ppd_cache.h
@@ -11,7 +11,6 @@
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
-#include "base/sequenced_task_runner.h"
 #include "base/time/time.h"
 #include "chromeos/chromeos_export.h"
 
@@ -46,9 +45,7 @@ class CHROMEOS_EXPORT PpdCache : public base::RefCounted<PpdCache> {
   // Create and return a Ppdcache that uses cache_dir to store state.  If
   // cache_base_dir does not exist, it will be lazily created the first time the
   // cache needs to store state.
-  static scoped_refptr<PpdCache> Create(
-      const base::FilePath& cache_base_dir,
-      scoped_refptr<base::SequencedTaskRunner> disk_task_runner);
+  static scoped_refptr<PpdCache> Create(const base::FilePath& cache_base_dir);
 
   // Start a Find, looking, for an entry with the given key that is at most
   // |max_age| old.  |cb| will be invoked on the calling thread.