Move MHTML file writing out of the renderer main thread.

third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h

Index: third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h
diff --git a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h
index a73d816a9b847939191420e732d80bae70a49141..5591b99c765a75a3c4b2e1c4fa74bc686bc3788c 100644
--- a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h
+++ b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.h
@@ -35,6 +35,7 @@
 #include "wtf/HashMap.h"
 #include "wtf/Vector.h"
 #include "wtf/text/StringHash.h"
+#include <vector>
 
 namespace blink {
 
@@ -61,7 +62,7 @@ public:
     // MHTML document (see also rfc1341, section 7.2.1, "boundary" description).
     static void generateMHTMLHeader(
         const String& boundary, const String& title, const String& mimeType,
-        SharedBuffer& outputBuffer);
+        std::vector<char>& outputBuffer);

[carlosk, 2016/10/03 23:51:05]

Is it really OK to pass non const references in Blink? Or should I change this
to a pointer instead?

[carlosk, 2016/10/04 21:49:53]

Just for the record: I did ask dcheng@ directly about this and passing non-const
references is acceptable in Blink as it implies a safe, never null "pointer" to
an output argument.

 
     // Serializes SerializedResource as an MHTML part and appends it in
     // |outputBuffer|.
@@ -75,7 +76,7 @@ public:
     static void generateMHTMLPart(
         const String& boundary, const String& contentID,
         EncodingPolicy, const SerializedResource&,
-        SharedBuffer& outputBuffer);
+        std::vector<char>& outputBuffer);
 
     // Generates an MHTML footer and appends it to |outputBuffer|.
     //
@@ -84,7 +85,7 @@ public:
     // MHTML document (see also rfc1341, section 7.2.1, "boundary" description).
     static void generateMHTMLFooter(
         const String& boundary,
-        SharedBuffer& outputBuffer);
+        std::vector<char>& outputBuffer);
 
     typedef HeapHashMap<String, Member<ArchiveResource>> SubArchiveResources;