Add a CPDFFontSubsetter test for standard fonts

Add CPDFFontSubsetterTest.StandardFont, which shows that standard fonts
are not subsetted. They do not have embedded font files.

Bug: 476127152
Change-Id: I70fbb86c4314b62a14a82edf3332ba7580fbc6d7
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/143771
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Andy Phan <andyphan@chromium.org>

core/fpdfapi/edit/cpdf_fontsubsetter_embeddertest.cpp

diff --git a/core/fpdfapi/edit/cpdf_fontsubsetter_embeddertest.cpp b/core/fpdfapi/edit/cpdf_fontsubsetter_embeddertest.cpp
index 4e7748a..b972fcda 100644
--- a/core/fpdfapi/edit/cpdf_fontsubsetter_embeddertest.cpp
+++ b/core/fpdfapi/edit/cpdf_fontsubsetter_embeddertest.cpp
@@ -243,6 +243,21 @@
               IsEmpty());
 }
 
+TEST_F(CPDFFontSubsetterTest, StandardFont) {
+  CreateEmptyDocument();
+  ScopedFPDFPage page(FPDFPage_New(document(), 0, 400, 400));
+
+  ScopedFPDFFont font(FPDFText_LoadStandardFont(document(), "Helvetica"));
+  ASSERT_TRUE(font);
+
+  ASSERT_NO_FATAL_FAILURE(
+      InsertNewTextObject(L"Hello world", page.get(), font.get()));
+
+  CPDF_FontSubsetter subsetter(CPDFDocumentFromFPDFDocument(document()));
+  EXPECT_THAT(subsetter.GenerateObjectOverrides(GetTestNewObjNums()),
+              IsEmpty());
+}
+
 TEST_F(CPDFFontSubsetterTest, OpenType) {
   CreateEmptyDocument();
   ScopedFPDFPage page(FPDFPage_New(document(), 0, 400, 400));