Bug 1527235 - Fix how the alpha channel was missing from pasted clipboard images. r=tnikkel

In order to get the alpha channel when encoding BMP images from a
surface, we need to supply bmp=32 in the encoder options.

Differential Revision: https://phabricator.services.mozilla.com/D19835

widget/windows/nsDataObj.cpp

@@ -825,7 +825,7 @@ nsDataObj::GetDib(const nsACString& inFlavor, FORMATETC& aFormat,
   nsCOMPtr<imgITools> imgTools =
       do_CreateInstance("@mozilla.org/image/tools;1");
 
-  nsAutoString options;
+  nsAutoString options(NS_LITERAL_STRING("bpp=32;"));
   if (aFormat.cfFormat == CF_DIBV5) {
     options.AppendLiteral("version=5");
   } else {
@@ -1445,7 +1445,7 @@ HRESULT nsDataObj::DropImage(FORMATETC& aFE, STGMEDIUM& aSTG) {
         do_CreateInstance("@mozilla.org/image/tools;1");
     nsCOMPtr<nsIInputStream> inputStream;
     rv = imgTools->EncodeImage(image, NS_LITERAL_CSTRING(IMAGE_BMP),
-                               NS_LITERAL_STRING("version=3"),
+                               NS_LITERAL_STRING("bpp=32;version=3"),
                                getter_AddRefs(inputStream));
     if (NS_FAILED(rv) || !inputStream) {
       return E_FAIL;