Remove stl_util's deletion function use from pdf/.

pdf/pdfium/pdfium_engine.h

Index: pdf/pdfium/pdfium_engine.h
diff --git a/pdf/pdfium/pdfium_engine.h b/pdf/pdfium/pdfium_engine.h
index 89406c7dd3711fe807e51cd136efd61fcbd53f40..8f8609ad623b15b5cf702b85338b87ce16ca402c 100644
--- a/pdf/pdfium/pdfium_engine.h
+++ b/pdf/pdfium/pdfium_engine.h
@@ -620,10 +620,8 @@ class PDFiumEngine : public PDFEngine,
   // on the page.
   FPDF_FORMHANDLE form_;
 
-  // The page(s) of the document. Store a vector of pointers so that when the
-  // vector is resized we don't close the pages that are used in pending
-  // paints.
-  std::vector<PDFiumPage*> pages_;
+  // The page(s) of the document.
+  std::vector<std::unique_ptr<PDFiumPage>> pages_;
 
   // The indexes of the pages currently visible.
   std::vector<int> visible_pages_;