Move closure_blocks_leopard_compat to base now that it's used by two modules.

content/browser/mac/closure_blocks_leopard_compat.h

-// Copyright (c) 2011 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.
-
-#ifndef CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_
-#define CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_
-#pragma once
-
-// libclosure (blocks) compatibility for Mac OS X 10.5 (Leopard)
-//
-// Background material:
-// http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Blocks
-// http://opensource.apple.com/source/libclosure/libclosure-38/
-//
-// Leopard doesn't support blocks. Chrome supports Leopard. Chrome needs to use
-// blocks.
-//
-// In any file where you use blocks (any time you type ^{...}), you must
-// #include this file to ensure that the runtime symbols referenced by code
-// emitted by the compiler are marked for weak-import. This means that if
-// these symbols are not present at runtime, the program will still load, but
-// their values will be NULL.
-//
-// In any target (in the GYP sense) where you use blocks, you must also depend
-// on the closure_blocks_leopard_compat target to ensure that these symbols
-// will be available at link time, even when the 10.5 SDK is in use. This
-// allows the continued use of the 10.5 SDK, which does not contain these
-// symbols.
-//
-// This does not relieve you of the responsibility to not use blocks on
-// Leopard. Because runtime support for Blocks still isn't present on that
-// operating system, the weak-imported symbols will have value 0 and attempts
-// to do anything meaningful with them will fail or crash. You must take care
-// not to enter any codepath that uses blocks on Leopard. The base::mac::IsOS*
-// family may be helpful.
-//
-// Although this scheme allows the use of the 10.5 SDK and 10.5 runtime in an
-// application that uses blocks, it is still necessary to use a compiler that
-// supports blocks. GCC 4.2 as shipped with Xcode 3.2 for Mac OS X 10.6
-// qualifies, as do sufficiently recent versions of clang. GCC 4.2 as shipped
-// with Xcode 3.1 for Mac OS X 10.5 does not qualify.
-
-// _NSConcreteGlobalBlock and _NSConcreteStackBlock are private implementation
-// details of libclosure defined in libclosure/libclosure-38/Block_private.h,
-// but they're exposed from libSystem as public symbols, and the block-enabled
-// compiler will emit code that references these symbols. Because the symbols
-// aren't present in 10.5's libSystem, they must be declared as weak imports
-// in any file that uses blocks. Any block-using file must #include this
-// header to guarantee that the symbols will show up in linked output as weak
-// imports when compiling for a 10.5 deployment target. Because the symbols
-// are always present in 10.6 and higher, they do not need to be a weak
-// imports when the deployment target is at least 10.6.
-//
-// Both GCC and clang emit references to these symbols, providing implicit
-// declarations as needed, but respecting any user declaration when present.
-// See gcc-5666.3/gcc/c-parser.c build_block_struct_initlist,
-// gcc-5666.3/gcc/cp/parser.c build_block_struct_initlist, and
-// clang-2.9/lib/CodeGen/CodeGenModule.cpp
-// CodeGenModule::getNSConcreteGlobalBlock() and
-// CodeGenModule::getNSConcreteStackBlock().
-
-#include <AvailabilityMacros.h>
-
-#if defined(MAC_OS_X_VERSION_10_6) && \
-    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6  // SDK >= 10.6
-// Get the system's own declarations of these things if using an SDK where
-// they are present.
-#include <Block.h>
-#endif  // SDK >= 10.6
-
-extern "C" {
-
-#if MAC_OS_X_VERSION_MIN_REQUIRED <= MAC_OS_X_VERSION_10_5  // DT <= 10.5
-#define MAYBE_WEAK_IMPORT __attribute__((weak_import))
-#else  // DT > 10.5
-#define MAYBE_WEAK_IMPORT
-#endif  // DT <= 10.5
-
-MAYBE_WEAK_IMPORT extern void* _Block_copy(const void*);
-MAYBE_WEAK_IMPORT extern void _Block_release(const void*);
-MAYBE_WEAK_IMPORT extern void _Block_object_assign(void*,
-                                                   const void*,
-                                                   const int);
-MAYBE_WEAK_IMPORT extern void _Block_object_dispose(const void*, const int);
-
-MAYBE_WEAK_IMPORT extern void* _NSConcreteGlobalBlock[32];
-MAYBE_WEAK_IMPORT extern void* _NSConcreteStackBlock[32];
-
-#undef MAYBE_WEAK_IMPORT
-
-}  // extern "C"
-
-// Macros from <Block.h>, in case <Block.h> is not present.
-
-#ifndef Block_copy
-#define Block_copy(...) \
-    ((__typeof(__VA_ARGS__))_Block_copy((const void *)(__VA_ARGS__)))
-#endif
-
-#ifndef Block_release
-#define Block_release(...) _Block_release((const void *)(__VA_ARGS__))
-#endif
-
-#endif  // CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_