Qualify |storage| namespace in some extensions code

There is both ::extensions::api::storage and ::storage so inside
extensions::api, unless you explicitly write ::storage it's unclear
what namespace is intended.

In jumbo builds, some code ended up in a translation unit where
both storage namespaces were known, so this patch adds ::
to storage to make the code explicit.

There is a code style guideline to not use namespace names that are
also top level namespace for this reason, but it's not easy to
change all extension api namespaces.

Bug: 850484
Change-Id: I1c85fbc9dd3dc8be49d41be25f4886ec98c47926
Reviewed-on: https://chromium-review.googlesource.com/1104678
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568116}

chrome/browser/extensions/api/developer_private/developer_private_api.h

@@ -614,7 +614,7 @@ class DeveloperPrivateLoadDirectoryFunction
   // ExtensionFunction:
   bool RunAsync() override;
 
-  bool LoadByFileSystemAPI(const storage::FileSystemURL& directory_url);
+  bool LoadByFileSystemAPI(const ::storage::FileSystemURL& directory_url);
 
   void ClearExistingDirectoryContent(const base::FilePath& project_path);
 
@@ -625,7 +625,7 @@ class DeveloperPrivateLoadDirectoryFunction
       const base::FilePath& project_path,
       const base::FilePath& destination_path,
       base::File::Error result,
-      storage::FileSystemOperation::FileEntryList file_list,
+      ::storage::FileSystemOperation::FileEntryList file_list,
       bool has_more);
 
   void SnapshotFileCallback(
@@ -633,14 +633,14 @@ class DeveloperPrivateLoadDirectoryFunction
       base::File::Error result,
       const base::File::Info& file_info,
       const base::FilePath& platform_path,
-      scoped_refptr<storage::ShareableFileReference> file_ref);
+      scoped_refptr<::storage::ShareableFileReference> file_ref);
 
   void CopyFile(const base::FilePath& src_path,
                 const base::FilePath& dest_path);
 
   void Load();
 
-  scoped_refptr<storage::FileSystemContext> context_;
+  scoped_refptr<::storage::FileSystemContext> context_;
 
   // syncfs url representing the root of the folder to be copied.
   std::string project_base_url_;