Fix nits involving 'constexpr const' code.

- Mark constants not in anonymous namespaces as static.
- Rename constants to kFoo.
- Remove constexpr or const if having both is redundant.
- Change one unsigned long variable to size_t.

Change-Id: Id1fb2f2d56ec659622123546b8c709f9df3f8caf
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/52873
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/fpdfsdk/fpdf_ppo_embeddertest.cpp b/fpdfsdk/fpdf_ppo_embeddertest.cpp
index 8b36045..8072d86 100644
--- a/fpdfsdk/fpdf_ppo_embeddertest.cpp
+++ b/fpdfsdk/fpdf_ppo_embeddertest.cpp
@@ -103,7 +103,7 @@
 TEST_F(FPDFPPOEmbedderTest, NupRenderImage) {
   ASSERT_TRUE(OpenDocument("rectangles_multi_pages.pdf"));
   const int kPageCount = 2;
-  constexpr const char* kExpectedMD5s[kPageCount] = {
+  static constexpr const char* kExpectedMD5s[kPageCount] = {
       "4d225b961da0f1bced7c83273e64c9b6", "fb18142190d770cfbc329d2b071aee4d"};
   ScopedFPDFDocument output_doc_3up(
       FPDF_ImportNPagesToOne(document(), 792, 612, 3, 1));