Use iosfwd in more headers.

Forward declaring shaves compilation costs down 1%.

Change-Id: Iea0c1d73db25327ebd4de8e895f912181774a670
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/79991
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fpdfapi/edit/cpdf_contentstream_write_utils.h b/core/fpdfapi/edit/cpdf_contentstream_write_utils.h
index 3e14c9f..c94e99e 100644
--- a/core/fpdfapi/edit/cpdf_contentstream_write_utils.h
+++ b/core/fpdfapi/edit/cpdf_contentstream_write_utils.h
@@ -5,7 +5,7 @@
 #ifndef CORE_FPDFAPI_EDIT_CPDF_CONTENTSTREAM_WRITE_UTILS_H_
 #define CORE_FPDFAPI_EDIT_CPDF_CONTENTSTREAM_WRITE_UTILS_H_
 
-#include <ostream>
+#include <iosfwd>
 
 #include "core/fxcrt/fx_coordinates.h"