Check page_number is in range in PdfMetafileCg::RenderPage().

Change-Id: I92e185b74416da823d9d697de05494de3c4bd65a
Reviewed-on: https://chromium-review.googlesource.com/774689Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517170}

printing/pdf_metafile_cg_mac.cc

@@ -167,6 +167,11 @@ bool PdfMetafileCg::RenderPage(unsigned int page_number,
     return false;
   }
 
+  const unsigned int page_count = GetPageCount();
+  DCHECK_NE(page_count, 0U);
+  DCHECK_NE(page_number, 0U);
+  DCHECK_LE(page_number, page_count);
+
   CGPDFPageRef pdf_page = CGPDFDocumentGetPage(pdf_doc, page_number);
   CGRect source_rect = CGPDFPageGetBoxRect(pdf_page, kCGPDFCropBox);
   int pdf_src_rotation = CGPDFPageGetRotationAngle(pdf_page);