Bug 1415081 - part 7 - Fix the use of NS_ReadInputStreamToString in HTMLCanvasElement, r=smaug

dom/html/HTMLCanvasElement.cpp

@@ -961,20 +961,15 @@ HTMLCanvasElement::MozGetAsFileImpl(const nsAString& aName,
   NS_ENSURE_SUCCESS(rv, rv);
 
   uint64_t imgSize;
-  rv = stream->Available(&imgSize);
-  NS_ENSURE_SUCCESS(rv, rv);
-  NS_ENSURE_TRUE(imgSize <= UINT32_MAX, NS_ERROR_FILE_TOO_BIG);
-
   void* imgData = nullptr;
-  rv = NS_ReadInputStreamToBuffer(stream, &imgData, (uint32_t)imgSize);
+  rv = NS_ReadInputStreamToBuffer(stream, &imgData, -1, &imgSize);
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsCOMPtr<nsPIDOMWindowInner> win = do_QueryInterface(OwnerDoc()->GetScopeObject());
 
   // The File takes ownership of the buffer
   RefPtr<File> file =
-    File::CreateMemoryFile(win, imgData, (uint32_t)imgSize, aName, type,
-                           PR_Now());
+    File::CreateMemoryFile(win, imgData, imgSize, aName, type, PR_Now());
 
   file.forget(aResult);
   return NS_OK;