Move MHTML file writing out of the renderer main thread.

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

Index: third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
diff --git a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
index 09d61918d13cea2522f5b5893fedf9f19981290f..334f671a805c26baf968f19df69ce82a39d94c95 100644
--- a/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
+++ b/third_party/WebKit/Source/platform/mhtml/MHTMLArchive.cpp
@@ -45,12 +45,21 @@
 #include "wtf/text/Base64.h"
 #include "wtf/text/StringBuilder.h"
 
-namespace blink {
+namespace {
 
 const char* const quotedPrintable = "quoted-printable";
 const char* const base64 = "base64";
 const char* const binary = "binary";
 
+enum class Encoding {
+  QuotedPrintable,
+  Base64,
+  Binary,
+};
+}
+
+namespace blink {
+
 static String replaceNonPrintableCharacters(const String& text) {
   StringBuilder stringBuilder;
   for (size_t i = 0; i < text.length(); ++i) {
@@ -110,7 +119,7 @@ bool MHTMLArchive::canLoadArchive(const KURL& url) {
 void MHTMLArchive::generateMHTMLHeader(const String& boundary,
                                        const String& title,
                                        const String& mimeType,
-                                       SharedBuffer& outputBuffer) {
+                                       std::vector<char>& outputBuffer) {
   ASSERT(!boundary.isEmpty());
   ASSERT(!mimeType.isEmpty());
 
@@ -142,14 +151,16 @@ void MHTMLArchive::generateMHTMLHeader(const String& boundary,
   ASSERT(stringBuilder.toString().containsOnlyASCII());
   CString asciiString = stringBuilder.toString().utf8();
 
-  outputBuffer.append(asciiString.data(), asciiString.length());
+  outputBuffer.reserve(outputBuffer.size() + asciiString.length());
+  outputBuffer.insert(outputBuffer.end(), asciiString.data(),
+                      asciiString.data() + asciiString.length());
 }
 
 void MHTMLArchive::generateMHTMLPart(const String& boundary,
                                      const String& contentID,
                                      EncodingPolicy encodingPolicy,
                                      const SerializedResource& resource,
-                                     SharedBuffer& outputBuffer) {
+                                     std::vector<char>& outputBuffer) {
   ASSERT(!boundary.isEmpty());
   ASSERT(contentID.isEmpty() || contentID[0] == '<');
 
@@ -168,17 +179,22 @@ void MHTMLArchive::generateMHTMLPart(const String& boundary,
     stringBuilder.append("\r\n");
   }
 
-  const char* contentEncoding = 0;
-  if (encodingPolicy == UseBinaryEncoding)
-    contentEncoding = binary;
-  else if (MIMETypeRegistry::isSupportedJavaScriptMIMEType(resource.mimeType) ||
-           MIMETypeRegistry::isSupportedNonImageMIMEType(resource.mimeType))
-    contentEncoding = quotedPrintable;
-  else
-    contentEncoding = base64;
+  const char* contentEncodingText = 0;
+  Encoding encoding = Encoding::Base64;
+  if (encodingPolicy == UseBinaryEncoding) {
+    contentEncodingText = binary;
+    encoding = Encoding::Binary;
+  } else if (MIMETypeRegistry::isSupportedJavaScriptMIMEType(
+                 resource.mimeType) ||
+             MIMETypeRegistry::isSupportedNonImageMIMEType(resource.mimeType)) {
+    contentEncodingText = quotedPrintable;
+    encoding = Encoding::QuotedPrintable;
+  } else {
+    contentEncodingText = base64;
+  }
 
   stringBuilder.append("Content-Transfer-Encoding: ");
-  stringBuilder.append(contentEncoding);
+  stringBuilder.append(contentEncodingText);
   stringBuilder.append("\r\n");
 
   if (!resource.url.protocolIsAbout()) {
@@ -190,13 +206,25 @@ void MHTMLArchive::generateMHTMLPart(const String& boundary,
   stringBuilder.append("\r\n");
 
   CString asciiString = stringBuilder.toString().utf8();
-  outputBuffer.append(asciiString.data(), asciiString.length());
 
-  if (!strcmp(contentEncoding, binary)) {
+  // Best guess for a reserved size. It should work well for binary and base64
+  // (see https://en.wikipedia.org/wiki/Base64#MIME); not so much for
+  // quoted-printable which is harder to estimate.
+  std::size_t expectedFinalSize = outputBuffer.size() + asciiString.length();
+  if (encoding == Encoding::Base64)
+    expectedFinalSize += static_cast<std::size_t>(resource.data->size() * 1.37);
+  else
+    expectedFinalSize += resource.data->size();
+  outputBuffer.reserve(expectedFinalSize);
+
+  outputBuffer.insert(outputBuffer.end(), asciiString.data(),
+                      asciiString.data() + asciiString.length());
+
+  if (encoding == Encoding::Binary) {
     const char* data;
     size_t position = 0;
     while (size_t length = resource.data->getSomeData(data, position)) {
-      outputBuffer.append(data, length);
+      outputBuffer.insert(outputBuffer.end(), data, data + length);
       position += length;
     }
   } else {
@@ -205,12 +233,14 @@ void MHTMLArchive::generateMHTMLPart(const String& boundary,
     const char* data = resource.data->data();
     size_t dataLength = resource.data->size();
     Vector<char> encodedData;
-    if (!strcmp(contentEncoding, quotedPrintable)) {
+    if (encoding == Encoding::QuotedPrintable) {
       quotedPrintableEncode(data, dataLength, encodedData);
-      outputBuffer.append(encodedData.data(), encodedData.size());
-      outputBuffer.append("\r\n", 2u);
+      outputBuffer.insert(outputBuffer.end(), encodedData.data(),
+                          encodedData.data() + encodedData.size());
+      outputBuffer.push_back('\r');
+      outputBuffer.push_back('\n');
     } else {
-      ASSERT(!strcmp(contentEncoding, base64));
+      DCHECK(encoding == Encoding::Base64);
       // We are not specifying insertLFs = true below as it would cut the lines
       // with LFs and MHTML requires CRLFs.
       base64Encode(data, dataLength, encodedData);
@@ -220,8 +250,10 @@ void MHTMLArchive::generateMHTMLPart(const String& boundary,
       do {
         size_t lineLength =
             std::min(encodedDataLength - index, maximumLineLength);
-        outputBuffer.append(encodedData.data() + index, lineLength);
-        outputBuffer.append("\r\n", 2u);
+        outputBuffer.insert(outputBuffer.end(), encodedData.data() + index,
+                            encodedData.data() + index + lineLength);
+        outputBuffer.push_back('\r');
+        outputBuffer.push_back('\n');
         index += maximumLineLength;
       } while (index < encodedDataLength);
     }
@@ -229,10 +261,12 @@ void MHTMLArchive::generateMHTMLPart(const String& boundary,
 }
 
 void MHTMLArchive::generateMHTMLFooter(const String& boundary,
-                                       SharedBuffer& outputBuffer) {
+                                       std::vector<char>& outputBuffer) {
   ASSERT(!boundary.isEmpty());
   CString asciiString = String("--" + boundary + "--\r\n").utf8();
-  outputBuffer.append(asciiString.data(), asciiString.length());
+  outputBuffer.reserve(outputBuffer.size() + asciiString.length());
+  outputBuffer.insert(outputBuffer.end(), asciiString.data(),
+                      asciiString.data() + asciiString.length());
 }
 
 void MHTMLArchive::setMainResource(ArchiveResource* mainResource) {