Refactor MHTMLGenerator to allow getting sending the data to a file descriptor.

content/browser/download/mhtml_generation_browsertest.cc

Index: content/browser/download/mhtml_generation_browsertest.cc
diff --git a/content/browser/download/mhtml_generation_browsertest.cc b/content/browser/download/mhtml_generation_browsertest.cc
index 7e99fb268574ac4d30b6941580286cfa66938c7c..6e790135bce5df3dc333b9821d651095e6eb4372 100644
--- a/content/browser/download/mhtml_generation_browsertest.cc
+++ b/content/browser/download/mhtml_generation_browsertest.cc
@@ -21,7 +21,7 @@ class MHTMLGenerationTest : public ContentBrowserTest {
  public:
   MHTMLGenerationTest() : mhtml_generated_(false), file_size_(0) {}
 
-  void MHTMLGenerated(const base::FilePath& path, int64 size) {
+  void MHTMLGenerated(int64 size) {
     mhtml_generated_ = true;
     file_size_ = size;
     base::MessageLoopForUI::current()->Quit();