Default to c++11 instead of c++14.

PDFium has users that may not be ready for C++14 yet.

Change-Id: I99de1c8126fd94ac728653262c05e5d26b1734f3
Reviewed-on: https://pdfium-review.googlesource.com/14351
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/.gn b/.gn
index 542ee5b..41187fd 100644
--- a/.gn
+++ b/.gn
@@ -11,4 +11,7 @@
 
   # Turns on compiler optimizations in V8 in Debug build.
   v8_optimized_debug = true
+
+  # PDFium does not want to switch to C++14 yet.
+  use_cxx11 = true
 }