Extracting and unittesting PrepareDropDataForChildProcess function.

content/browser/fileapi/browser_file_system_helper.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_FILEAPI_BROWSER_FILE_SYSTEM_HELPER_H_
 #define CONTENT_BROWSER_FILEAPI_BROWSER_FILE_SYSTEM_HELPER_H_
 
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "storage/browser/fileapi/file_system_context.h"
 
 namespace storage {
 class FileSystemContext;
 class FileSystemURL;
 }
 
 namespace content {
 
 class BrowserContext;
+class ChildProcessSecurityPolicyImpl;
+struct DropData;
 
 // Helper method that returns FileSystemContext constructed for
 // the browser process.
 CONTENT_EXPORT scoped_refptr<storage::FileSystemContext>
     CreateFileSystemContext(BrowserContext* browser_context,
                             const base::FilePath& profile_path,
                             bool is_incognito,
                             storage::QuotaManagerProxy* quota_manager_proxy);
 
 // Verifies that |url| is valid and has a registered backend in |context|.
 CONTENT_EXPORT bool FileSystemURLIsValid(storage::FileSystemContext* context,
                                          const storage::FileSystemURL& url);
 
 // Get the platform path from a file system URL. This needs to be called
 // on the FILE thread.
 CONTENT_EXPORT void SyncGetPlatformPath(storage::FileSystemContext* context,
                                         int process_id,
                                         const GURL& path,
                                         base::FilePath* platform_path);
+

[ncarter (slow), 2017/04/24 22:01:51]

Maybe this as an intro sentence:

// Make it possible for a |drop_data|'s resources to be read by |child_id|'s
// process -- by granting permissions, rewriting |drop_data|, or both.
//

[Łukasz Anforowicz, 2017/04/24 22:18:10]

Done.

+// |drop_data| can include references to local files and filesystem files that
+// were accessible to the child process that is the source of the drag and drop,
+// but might not (yet) be accessible the child process that is the target of the
+// drop.  PrepareDropDataForChildProcess makes sure that |child_id| has access
+// to files referred to by |drop_data| - this method will 1) mutate |drop_data|
+// as needed (e.g. to refer to files in a new isolated filesystem, rather than
+// the original filesystem files) and 2) use |security_policy| to grant
+// |child_id| appropriate file access.
+CONTENT_EXPORT void PrepareDropDataForChildProcess(

[Łukasz Anforowicz, 2017/04/24 21:30:24]

TBH I don't understand why |CONTENT_EXPORT| is needed here.  I am guessing that
things don't link without it, because there is an (unexpected to me) component
build boundary between here and
content/browser/renderer_host/render_widget_host_impl.cc.  FWIW, other
content-internal things in this file use CONTENT_EXPORT, so this is probably
fine.

[ncarter (slow), 2017/04/24 22:01:51]

In the component build, both render_widget_host_impl.cc and
browser_file_system_helper.cc get compiled into content.dll. If you didn't have
a unittest, you wouldn't need CONTENT_EXPORT.

You need the CONTENT_EXPORT because otherwise your unittest (which calls this
function directly) doesn't know to look in content.dll for this function.

[Łukasz Anforowicz, 2017/04/24 22:18:10]

Oh, ok - thanks for the explanation.  I guess I should have looked closer at the
error message from the linker to realize that it is complaining about the unit
tests, not about the product code.

+    DropData* drop_data,
+    ChildProcessSecurityPolicyImpl* security_policy,

[Łukasz Anforowicz, 2017/04/24 21:30:23]

This has to be CPSPImpl, because CPSP doesn't expose
GrantRequestSpecificFileURL.

[ncarter (slow), 2017/04/24 22:01:51]

That's fine.

+    int child_id,
+    const storage::FileSystemContext* file_system_context);
+
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FILEAPI_BROWSER_FILE_SYSTEM_HELPER_H_