Share precompiled header setup for blink between Windows and Mac.

third_party/WebKit/Source/platform/mac/Precompile-platform.h

Index: third_party/WebKit/Source/platform/mac/Precompile-platform.h
diff --git a/third_party/WebKit/Source/platform/mac/Precompile-platform.h b/third_party/WebKit/Source/platform/mac/Precompile-platform.h
new file mode 100644
index 0000000000000000000000000000000000000000..570521711438addd74ab1b6c76a0a2c9e09a6e40
--- /dev/null
+++ b/third_party/WebKit/Source/platform/mac/Precompile-platform.h
@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+#if defined(PrecompilePlatform_h_)

[Nico, 2017/03/02 16:59:14]

Can we make it so that we have a platform/Precompile-platform.h header only, and
not one copy per platform? It could look like

#if defined...
...

#if defined(_MSC_VER)
#include "build/win/Precompile.h"
#elif defined(__APPLE__)
#include "build/mac/Prefix.h"
#else
#error implement
#endif

...

+#error You shouldn't include the precompiled header file more than once.
+#endif
+
+#define PrecompilePlatform_h_
+
+#include "build/mac/Prefix.h"
+
+// Include Oilpan's Handle.h by default, as it is included by a significant
+// portion of platform/ source files.
+#include "platform/heap/Handle.h"