Add optional public header checking to GN build

third_party/modp_b64/README.chromium

Index: third_party/modp_b64/README.chromium
diff --git a/third_party/modp_b64/README.chromium b/third_party/modp_b64/README.chromium
index 26eed1e80c8befa33947be3fe770c135447d1c8f..35b9e548408276bb49394224584719c2a22f34f7 100644
--- a/third_party/modp_b64/README.chromium
+++ b/third_party/modp_b64/README.chromium
@@ -11,12 +11,5 @@ and to fix compilation errors that occur under VC8.  The file was renamed
 modp_b64.cc to force it to be compiled as C++ so that the inclusion of
 basictypes.h could be possible.
 
-The file modp_b64_data.h was generated by modp_b64_gen.c (under Linux),
-which is not included in this directory.  The resulting header was
-modified to not include <stdint.h> when COMPILER_MSVC is defined (since
-that header file does not exist under VC8), but instead in that case to
-include "base/basictypes.h" and provide the required typedefs for
-uint8_t and uint32_t using uint8 and uint32.
-
 The modp_b64.cc and modp_b64.h files were modified to make them safe on
-64-bit systems.
+64-bit systems.