Ensure the RendererAppContainer feature always has one instance

Make it static otherwise its memory address might change between
IsAppContainerEnabled() calls and would break pointer-based identity
lookup.

R=forshaw@chromium.org

Change-Id: I775dca403a317c32ced5bd998c152849ca0413a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449471Reviewed-by: James Forshaw <forshaw@chromium.org>
Commit-Queue: James Forshaw <forshaw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814319}

AUTHORS

@@ -794,6 +794,7 @@ Peter Gal <pgal.u-szeged@partner.samsung.com>
 Peter Griffin <peter.griffin@linaro.org>
 Peter Molnar <pmolnar.u-szeged@partner.samsung.com>
 Peter Snyder <snyderp@gmail.com>
+Peter Varga <pvarga@inf.u-szeged.hu>
 Peter Wong <peter.wm.wong@gmail.com>
 Philip Hanson <philip.hanson@intel.com>
 Philipp Hancke <fippo@andyet.net>

sandbox/policy/win/sandbox_win.cc

@@ -577,8 +577,10 @@ bool IsAppContainerEnabled() {
   if (base::win::GetVersion() < base::win::Version::WIN8)
     return false;
 
-  return base::FeatureList::IsEnabled(
-      {"RendererAppContainer", base::FEATURE_DISABLED_BY_DEFAULT});
+  static const base::Feature kRendererAppContainer{
+      "RendererAppContainer", base::FEATURE_DISABLED_BY_DEFAULT};
+
+  return base::FeatureList::IsEnabled(kRendererAppContainer);
 }
 
 ResultCode SetJobMemoryLimit(const base::CommandLine& cmd_line,