Add first pixel diffing test.

testing/resources/pixel/font_size.in

Index: testing/resources/pixel/font_size.in
diff --git a/testing/resources/pixel/font_size.in b/testing/resources/pixel/font_size.in
new file mode 100644
index 0000000000000000000000000000000000000000..c4e21e235866f05cb805dcda3ae7ba5c537dcdd1
--- /dev/null
+++ b/testing/resources/pixel/font_size.in
@@ -0,0 +1,62 @@
+{{header}}
+{{object 1 0}} <<
+  /Type /Catalog
+  /Pages 2 0 R
+>>
+{{object 2 0}} <<
+  /Type /Pages
+  /MediaBox [ 0 0 100 400 ]
+  /Count 1
+  /Kids [ 3 0 R ]
+>>
+endobj
+{{object 3 0}} <<
+  /Type /Page
+  /Parent 2 0 R
+  /Resources <<
+    /Font <<
+      /F1 4 0 R
+    >>
+  >>
+  /Contents 6 0 R
+>>
+endobj
+{{object 4 0}} <<
+  /Type /Font
+  /Subtype /Type1
+  /BaseFont /Times-Roman
+>>
+endobj
+{{object 6 0}} <<
+>>
+stream
+BT
+20 0 Td
+0 20 Td /F1 0 Tf (Size 0) Tj
+0 20 Td /F1 1 Tf (Size 1) Tj
+0 20 Td /F1 2 Tf (Size 2) Tj
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+0 20 Td /F1 4 Tf (Size 4) Tj
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+0 20 Td /F1 6 Tf (Size 6) Tj
+0 20 Td /F1 7 Tf (Size 7) Tj
+0 20 Td /F1 8 Tf (Size 8) Tj
+0 20 Td /F1 9 Tf (Size 9) Tj
+0 20 Td /F1 10 Tf (Size 10) Tj
+0 20 Td /F1 11 Tf (Size 11) Tj
+0 20 Td /F1 12 Tf (Size 12) Tj
+0 20 Td /F1 13 Tf (Size 13) Tj
+0 20 Td /F1 14 Tf (Size 14) Tj
+0 20 Td /F1 15 Tf (Size 15) Tj
+0 20 Td /F1 16 Tf (Size 16) Tj
+0 20 Td /F1 17 Tf (Size 17) Tj
+0 20 Td /F1 18 Tf (Size 18) Tj
+ET
+endstream
+endobj
+{{xref}}
+trailer <<
+  /Root 1 0 R
+>>
+{{startxref}}
+%%EOF