PpdProvider v3: anonymize PpdMetadataManagerImpl

This change moves the PpdMetadataManagerImpl into the anonymous
namespace where it was originally intended to go.

Bug: chromium:888189
Test: autoninja ... chrome{,os_unittests}
Change-Id: I701f50c498a75123ad5a49bc3524fe2e575aaa76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315494Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Kalvin Lee <kdlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794325}

chromeos/printing/ppd_metadata_manager.cc

@@ -295,8 +295,6 @@ std::string PpdMetadataPathInServingRoot(
   return std::string();
 }
 
-}  // namespace
-
 // Note: generally, each Get*() method is segmented into three parts:
 // 1. check if query can be answered immediately,
 // 2. fetch appropriate metadata if it can't [defer to On*Fetched()],
@@ -708,6 +706,8 @@ class PpdMetadataManagerImpl : public PpdMetadataManager {
   base::WeakPtrFactory<PpdMetadataManagerImpl> weak_factory_;
 };
 
+}  // namespace
+
 // static
 std::unique_ptr<PpdMetadataManager> PpdMetadataManager::Create(
     base::StringPiece browser_locale,