Delete the temporary file when generating MHTML with the extension API.

chrome/renderer/resources/extensions/extension_process_bindings.js

Index: chrome/renderer/resources/extensions/extension_process_bindings.js
diff --git a/chrome/renderer/resources/extensions/extension_process_bindings.js b/chrome/renderer/resources/extensions/extension_process_bindings.js
index 96db3680440ac2be55915a2ea65468198c0fe7c2..18ab836a44cd20a22cb5951a414660b8d77d71a1 100644
--- a/chrome/renderer/resources/extensions/extension_process_bindings.js
+++ b/chrome/renderer/resources/extensions/extension_process_bindings.js
@@ -24,6 +24,7 @@ var chrome = chrome || {};
   native function GetLocalFileSystem(name, path);
   native function DecodeJPEG(jpegImage);
   native function CreateBlob(filePath);
+  native function SendResponseAck(requestId);
 
   var chromeHidden = GetChromeHidden();
 
@@ -178,6 +179,7 @@ var chrome = chrome || {};
     var nativeFunction = opt_args.nativeFunction || StartRequest;
 
     var requestId = GetNextRequestId();
+    request.id = requestId;
     requests[requestId] = request;
     var hasCallback =
         (request.callback || opt_args.customCallback) ? true : false;
@@ -766,8 +768,11 @@ var chrome = chrome || {};
 
         if (request.callback)
           request.callback(CreateBlob(path, size));
-
         request.callback = null;
+
+        // Notify the browser. Now that the blob is referenced from JavaScript,
+        // the browser can drop its reference to it.
+        SendResponseAck(request.id);
       };
 
     apiFunctions["fileBrowserPrivate.requestLocalFileSystem"].customCallback =