Move MHTML file writing out of the renderer main thread.

third_party/WebKit/Source/web/WebFrameSerializer.cpp

Index: third_party/WebKit/Source/web/WebFrameSerializer.cpp
diff --git a/third_party/WebKit/Source/web/WebFrameSerializer.cpp b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
index 15923ed2b070310f3f3808b2174505bed1b4a916..09f54b4ad095b500b2deee98bb78b1016f0456f3 100644
--- a/third_party/WebKit/Source/web/WebFrameSerializer.cpp
+++ b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
@@ -179,7 +179,7 @@ bool frameShouldBeSerializedAsMHTML(WebLocalFrame* frame, WebFrameSerializerCach
 
 } // namespace
 
-WebData WebFrameSerializer::generateMHTMLHeader(
+std::vector<char> WebFrameSerializer::generateMHTMLHeader(
     const WebString& boundary, WebLocalFrame* frame, MHTMLPartsGenerationDelegate* delegate)
 {
     TRACE_EVENT0("page-serialization", "WebFrameSerializer::generateMHTMLHeader");
@@ -187,21 +187,20 @@ WebData WebFrameSerializer::generateMHTMLHeader(
     DCHECK(delegate);
 
     if (!frameShouldBeSerializedAsMHTML(frame, delegate->cacheControlPolicy()))
-        return WebData();
+        return std::move(std::vector<char>());
 
     WebLocalFrameImpl* webLocalFrameImpl = toWebLocalFrameImpl(frame);
     DCHECK(webLocalFrameImpl);
 
     Document* document = webLocalFrameImpl->frame()->document();
 
-    RefPtr<SharedBuffer> buffer = SharedBuffer::create();
+    std::vector<char> output;
     MHTMLArchive::generateMHTMLHeader(
-        boundary, document->title(), document->suggestedMIMEType(),
-        *buffer);
-    return buffer.release();
+        boundary, document->title(), document->suggestedMIMEType(), output);
+    return std::move(output);
 }
 
-WebData WebFrameSerializer::generateMHTMLParts(
+std::vector<char> WebFrameSerializer::generateMHTMLParts(
     const WebString& boundary, WebLocalFrame* webFrame, MHTMLPartsGenerationDelegate* webDelegate)
 {
     TRACE_EVENT0("page-serialization", "WebFrameSerializer::generateMHTMLParts");
@@ -209,7 +208,7 @@ WebData WebFrameSerializer::generateMHTMLParts(
     DCHECK(webDelegate);
 
     if (!frameShouldBeSerializedAsMHTML(webFrame, webDelegate->cacheControlPolicy()))
-        return WebData();
+        return std::move(std::vector<char>());
 
     // Translate arguments from public to internal blink APIs.
     LocalFrame* frame = toWebLocalFrameImpl(webFrame)->frame();
@@ -233,7 +232,7 @@ WebData WebFrameSerializer::generateMHTMLParts(
     String frameContentID = webDelegate->getContentID(webFrame);
 
     // Encode serializer's output as MHTML.
-    RefPtr<SharedBuffer> output = SharedBuffer::create();
+    std::vector<char> output;
     {
         SCOPED_BLINK_UMA_HISTOGRAM_TIMER("PageSerialization.MhtmlGeneration.EncodingTime.SingleFrame");
         bool isFirstResource = true;
@@ -244,20 +243,20 @@ WebData WebFrameSerializer::generateMHTMLParts(
             String contentID = isFirstResource ? frameContentID : String();
 
             MHTMLArchive::generateMHTMLPart(
-                boundary, contentID, encodingPolicy, resource, *output);
+                boundary, contentID, encodingPolicy, resource, output);
 
             isFirstResource = false;
         }
     }
-    return output.release();
+    return std::move(output);
 }
 
-WebData WebFrameSerializer::generateMHTMLFooter(const WebString& boundary)
+std::vector<char> WebFrameSerializer::generateMHTMLFooter(const WebString& boundary)
 {
     TRACE_EVENT0("page-serialization", "WebFrameSerializer::generateMHTMLFooter");
-    RefPtr<SharedBuffer> buffer = SharedBuffer::create();
-    MHTMLArchive::generateMHTMLFooter(boundary, *buffer);
-    return buffer.release();
+    std::vector<char> output;
+    MHTMLArchive::generateMHTMLFooter(boundary, output);
+    return std::move(output);
 }
 
 bool WebFrameSerializer::serialize(