[cros] Add user image transparency support.

chrome/browser/chromeos/login/user_manager.cc

Index: chrome/browser/chromeos/login/user_manager.cc
diff --git a/chrome/browser/chromeos/login/user_manager.cc b/chrome/browser/chromeos/login/user_manager.cc
index 8f8277f46360a2e6b6e91c3ad3d575d417b6fef1..215b6c25b3973c52c155d2a3b001e4633fdbbcd4 100644
--- a/chrome/browser/chromeos/login/user_manager.cc
+++ b/chrome/browser/chromeos/login/user_manager.cc
@@ -770,7 +770,7 @@ void UserManager::SaveImageToFile(const std::string& username,
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 
   std::vector<unsigned char> encoded_image;
-  if (!gfx::PNGCodec::EncodeBGRASkBitmap(image, true, &encoded_image)) {
+  if (!gfx::PNGCodec::EncodeBGRASkBitmap(image, false, &encoded_image)) {
     LOG(ERROR) << "Failed to PNG encode the image.";
     return;
   }