[Offline Pages] Generate MHTML header in the browser process.

content/browser/download/mhtml_generation_manager.h

Index: content/browser/download/mhtml_generation_manager.h
diff --git a/content/browser/download/mhtml_generation_manager.h b/content/browser/download/mhtml_generation_manager.h
index e30001535b03735758e09f2734d69ce5cd1c03d7..f096d39c2b388b89cc22ee3897129aae2dfaa3c0 100644
--- a/content/browser/download/mhtml_generation_manager.h
+++ b/content/browser/download/mhtml_generation_manager.h
@@ -61,16 +61,22 @@ class MHTMLGenerationManager {
  private:
   friend struct base::DefaultSingletonTraits<MHTMLGenerationManager>;
   class Job;
+  struct FileCreationResult {
+    base::File file;
+    int header_size = 0;
+  };
 
   MHTMLGenerationManager();
   virtual ~MHTMLGenerationManager();
 
   // Called on the file thread to create |file|.

[carlosk, 2017/04/25 01:28:08]

Append "and write the MHTML header into it".

-  static base::File CreateFile(const base::FilePath& file_path);
+  static FileCreationResult CreateFileAndWriteHeader(
+      const base::FilePath& file_path,
+      const std::string& header);
 
   // Called on the UI thread when the file that should hold the MHTML data has
   // been created.
-  void OnFileAvailable(int job_id, base::File browser_file);
+  void OnFileAvailable(int job_id, FileCreationResult result);
 
   // Called on the UI thread when a job has been finished.
   void JobFinished(Job* job, MhtmlSaveStatus save_status);