Enable precompiled headers for Blink on Windows.

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

Index: third_party/WebKit/Source/platform/win/Precompile-platform.h
diff --git a/third_party/WebKit/Source/platform/win/Precompile-platform.h b/third_party/WebKit/Source/platform/win/Precompile-platform.h
new file mode 100644
index 0000000000000000000000000000000000000000..84bc4c879225dc0be44cf9daba02f17c127918e5
--- /dev/null
+++ b/third_party/WebKit/Source/platform/win/Precompile-platform.h
@@ -0,0 +1,15 @@
+// Copyright 2016 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_)
+#error You shouldn't include the precompiled header file more than once.
+#endif
+
+#define PrecompilePlatform_h_
+
+#include "build/win/Precompile.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"