Revert "[Gin] Add feature to do extra masking in V8."

This reverts commit e265c9c.

Reason for revert: Feature enabled by default so no longer required.

Original change's description:
> [Gin] Add feature to do extra masking in V8.
> 
> Change-Id: Iba70082c0c8cb01c8bcb8c5c6e7f0fa237184f30
> Reviewed-on: https://chromium-review.googlesource.com/834088
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#525316}

TBR=rmcilroy@chromium.org,jochen@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I67a4d9904106d143df7020f61e95378eb9a72b48
Reviewed-on: https://chromium-review.googlesource.com/852873
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527623}

gin/BUILD.gn

@@ -32,8 +32,6 @@ component("gin") {
     "function_template.cc",
     "function_template.h",
     "gin_export.h",
-    "gin_features.cc",
-    "gin_features.h",
     "handle.h",
     "interceptor.cc",
     "interceptor.h",

gin/v8_initializer.cc

@@ -25,7 +25,6 @@
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
-#include "gin/gin_features.h"
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 #if defined(OS_ANDROID)
@@ -232,14 +231,6 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode,
 
   v8::V8::InitializePlatform(V8Platform::Get());
 
-  if (base::FeatureList::IsEnabled(features::kV8ExtraMasking)) {
-    static const char extra_masking[] = "--extra-masking";
-    v8::V8::SetFlagsFromString(extra_masking, sizeof(extra_masking) - 1);
-  } else {
-    static const char no_extra_masking[] = "--no-extra-masking";
-    v8::V8::SetFlagsFromString(no_extra_masking, sizeof(no_extra_masking) - 1);
-  }
-
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);