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

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 7d999ec0c09d06191eaf7a5df81f225e8253fdfa..b6167b37ba08fd301d02d2a4c64a9500d6d8bc79 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -1929,8 +1929,8 @@ void WebContentsImpl::SaveFrame(const GURL& url,
 
 void WebContentsImpl::GenerateMHTML(
     const base::FilePath& file,
-    const base::Callback<void(const base::FilePath&, int64)>& callback) {
-  MHTMLGenerationManager::GetInstance()->GenerateMHTML(this, file, callback);
+    const base::Callback<void(int64)>& callback) {
+  MHTMLGenerationManager::GetInstance()->SaveMHTML(this, file, callback);
 }
 
 bool WebContentsImpl::IsActiveEntry(int32 page_id) {