[libplatform] Deprecate EnsureEventLoopInitialized

R=ulan@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Iaa9968945ce8196de75b4c4a637bda9ee57c0509
Reviewed-on: https://chromium-review.googlesource.com/1047207Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53104}

include/libplatform/libplatform.h

@@ -62,7 +62,7 @@ V8_PLATFORM_EXPORT bool PumpMessageLoop(
     v8::Platform* platform, v8::Isolate* isolate,
     MessageLoopBehavior behavior = MessageLoopBehavior::kDoNotWait);
 
-V8_PLATFORM_EXPORT V8_DEPRECATE_SOON(
+V8_PLATFORM_EXPORT V8_DEPRECATED(
     "This function has become obsolete and is essentially a nop",
     void EnsureEventLoopInitialized(v8::Platform* platform,
                                     v8::Isolate* isolate));