Add --stable-release-mode to content_shell

content/shell/common/shell_switches.cc

Index: content/shell/common/shell_switches.cc
diff --git a/content/shell/common/shell_switches.cc b/content/shell/common/shell_switches.cc
index 81a4a6844ad1d6d36aaf69a0c74758e35d6bd090..a00af4569728e8be0638e499d1095de10173e3ed 100644
--- a/content/shell/common/shell_switches.cc
+++ b/content/shell/common/shell_switches.cc
@@ -34,4 +34,10 @@ const char kExposeInternalsForTesting[]     = "expose-internals-for-testing";
 // Save results when layout-as-browser tests fail.
 const char kOutputLayoutTestDifferences[] = "output-layout-test-differences";
 
+// This makes us disable some web-platform runtime features so that we test
+// content_shell as if it was a stable release. It is only followed when
+// kDumpRenderTree is set. For the features' level, see
+// http://dev.chromium.org/blink/runtime-enabled-features.
+const char kStableReleaseMode[] = "stable-release-mode";
+
 }  // namespace switches