Add namespace and re-arrange PDFium's local copy of chromium /base.

third_party/base/macros.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains macros and macro-like constructs (e.g., templates) that
 // are commonly used throughout Chromium source. (It may also contain things
 // that are closely related to things that are commonly used that belong in this
 // file.)
 
-#ifndef BASE_MACROS_H_
-#define BASE_MACROS_H_
+#ifndef PDFIUM_THIRD_PARTY_BASE_MACROS_H_
+#define PDFIUM_THIRD_PARTY_BASE_MACROS_H_
 
 // The COMPILE_ASSERT macro can be used to verify that a compile time
 // expression is true. For example, you could use it to verify the
 // size of a static array:
 //
 //   COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES,
 //                  content_type_names_incorrect_size);
 //
 // or to make sure a struct is smaller than a certain size:
 //
 //   COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large);
 //
 // The second argument to the macro is the name of the variable. If
 // the expression is false, most compilers will issue a warning/error
 // containing the name of the variable.
 
 #undef COMPILE_ASSERT
 #define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
 
-#endif  // BASE_MACROS_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_MACROS_H_