Make "--diff" option handle reverse-byte-order results for pdfium_diff

This CL adds the support for running pdfium-diff with the "--diff"
option to compare the reverse-byte-order rendering result with the
baseline image so that it's easier to see the discrepancies.

Bug: pdfium:1955
Change-Id: I8b37975dfc902750722c82768489fefe66dc439b
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/109211
Commit-Queue: Nigi <nigi@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>

testing/image_diff/image_diff.cpp

diff --git a/testing/image_diff/image_diff.cpp b/testing/image_diff/image_diff.cpp
index a701921..d48c253 100644
--- a/testing/image_diff/image_diff.cpp
+++ b/testing/image_diff/image_diff.cpp
@@ -369,11 +369,17 @@
                const std::string& file1,
                const std::string& file2,
                const std::string& out_file,
-               bool do_subtraction) {
+               bool do_subtraction,
+               bool reverse_byte_order) {
   Image actual_image;
   Image baseline_image;
 
-  if (!actual_image.CreateFromFilename(file1)) {
+  bool actual_load_result =
+      reverse_byte_order
+          ? actual_image.CreateFromFilenameWithReverseByteOrder(file1)
+          : actual_image.CreateFromFilename(file1);
+
+  if (!actual_load_result) {
     fprintf(stderr, "%s: Unable to open file \"%s\"\n", binary_name.c_str(),
             file1.c_str());
     return kStatusError;
@@ -451,7 +457,7 @@
   if (produce_diff_image || produce_image_subtraction) {
     if (!diff_filename.empty()) {
       return DiffImages(binary_name, filename1, filename2, diff_filename,
-                        produce_image_subtraction);
+                        produce_image_subtraction, reverse_byte_order);
     }
   } else if (!filename2.empty()) {
     return CompareImages(binary_name, filename1, filename2, histograms,