Make (and verify) public/ files compile under C.

testing/embedder_test.cpp

 // Copyright (c) 2015 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "embedder_test.h"
 
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ skipping 148 matching lines @@
 }
 
 int Get_Block(void* param, unsigned long pos, unsigned char* pBuf,
               unsigned long size) {
   TestLoader* pLoader = (TestLoader*) param;
   if (pos + size < pos || pos + size > pLoader->m_Len) return 0;
   memcpy(pBuf, pLoader->m_pBuf + pos, size);
   return 1;
 }
 
-bool Is_Data_Avail(FX_FILEAVAIL* pThis, size_t offset, size_t size) {
+FPDF_BOOL Is_Data_Avail(FX_FILEAVAIL* pThis, size_t offset, size_t size) {
   return true;
 }
 
 void Add_Segment(FX_DOWNLOADHINTS* pThis, size_t offset, size_t size) {
 }
 
 EmbedderTest::EmbedderTest() :
       document_(nullptr),
       form_handle_(nullptr),
       avail_(nullptr),
@@ skipping 157 matching lines @@
 }
 
 // Can't use gtest-provided main since we need to stash the path to the
 // executable in order to find the external V8 binary data files.
 int main(int argc, char** argv) {
   g_exe_path_ = argv[0];
   testing::InitGoogleTest(&argc, argv);
   testing::InitGoogleMock(&argc, argv);
   return RUN_ALL_TESTS();
 }