Reland "fuchsia: Set up for 3-sided roll to convert Magenta->Zircon"

This is a reland of aabb893a
Original change's description:
> fuchsia: Set up for 3-sided roll to convert Magenta->Zircon
> 
> Fuchsia changed their kernel name from Magenta to Zircon and all the
> functions and defines along with it. In order to be able to roll the SDK
> in Chromium, we first need to land with this define added in v8, so that
> can roll in to Chromium, then roll the Fuchsia SDK with this magic
> define set (CHROMIUM_ROLLING_MAGENTA_TO_ZIRCON), then actually update v8
> to reference zx_ instead of mx_ and roll that again.
> 
> Chromium-side for reference: https://chromium-review.googlesource.com/c/chromium/src/+/669139
> 
> Bug: chromium:765754, chromium:707030
> Change-Id: I4ed5027f455d2346f431e7c700e87693348d5b79
> Reviewed-on: https://chromium-review.googlesource.com/668751
> Reviewed-by: Bill Budge <bbudge@chromium.org>
> Commit-Queue: Scott Graham <scottmg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48047}

TBR=bbudge@chromium.org

Bug: chromium:765754, chromium:707030
Change-Id: Ib6e99ca418af527014622614d07d295b6110f9d5
Reviewed-on: https://chromium-review.googlesource.com/670944Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48067}

src/base/platform/platform-fuchsia.cc

@@ -2,8 +2,28 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// TODO(scottmg): Temporary during 3-sided roll, see https://crbug.com/765754.
+#if defined(CHROMIUM_ROLLING_MAGENTA_TO_ZIRCON)
+#include <zircon/process.h>
+#include <zircon/syscalls.h>
+#define MX_OK ZX_OK
+#define MX_PROP_NAME ZX_PROP_NAME
+#define MX_VM_FLAG_PERM_EXECUTE ZX_VM_FLAG_PERM_EXECUTE
+#define MX_VM_FLAG_PERM_READ ZX_VM_FLAG_PERM_READ
+#define MX_VM_FLAG_PERM_WRITE ZX_VM_FLAG_PERM_WRITE
+#define mx_handle_close zx_handle_close
+#define mx_handle_t zx_handle_t
+#define mx_object_set_property zx_object_set_property
+#define mx_status_t zx_status_t
+#define mx_vmar_map zx_vmar_map
+#define mx_vmar_protect zx_vmar_protect
+#define mx_vmar_root_self zx_vmar_root_self
+#define mx_vmar_unmap zx_vmar_unmap
+#define mx_vmo_create zx_vmo_create
+#else
 #include <magenta/process.h>
 #include <magenta/syscalls.h>
+#endif
 
 #include "src/base/macros.h"
 #include "src/base/platform/platform-posix-time.h"
@@ -162,3 +182,20 @@ bool VirtualMemory::HasLazyCommits() {
 
 }  // namespace base
 }  // namespace v8
+
+#if defined(CHROMIUM_ROLLING_MAGENTA_TO_ZIRCON)
+#undef MX_OK ZX_OK
+#undef MX_PROP_NAME ZX_PROP_NAME
+#undef MX_VM_FLAG_PERM_EXECUTE ZX_VM_FLAG_PERM_EXECUTE
+#undef MX_VM_FLAG_PERM_READ ZX_VM_FLAG_PERM_READ
+#undef MX_VM_FLAG_PERM_WRITE ZX_VM_FLAG_PERM_WRITE
+#undef mx_handle_close zx_handle_close
+#undef mx_handle_t zx_handle_t
+#undef mx_object_set_property zx_object_set_property
+#undef mx_status_t zx_status_t
+#undef mx_vmar_map zx_vmar_map
+#undef mx_vmar_protect zx_vmar_protect
+#undef mx_vmar_root_self zx_vmar_root_self
+#undef mx_vmar_unmap zx_vmar_unmap
+#undef mx_vmo_create zx_vmo_create
+#endif