ES6 modules: Enable by default with a kill switch

This patch enables ES6 modules support by default with a kill switch
that can be managed by about://flags and server providing configurations.

Bug: 736192
Change-Id: I5c244ba0103a95625aefc9b42e9295d03ff8d4a2
Reviewed-on: https://chromium-review.googlesource.com/558727
Reviewed-by: Kent Tamura <[email protected]>
Reviewed-by: Kouhei Ueno <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Commit-Queue: Takashi Toyoshima <[email protected]>
Cr-Commit-Position: refs/heads/master@{#484063}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index c2a35eb..c11915c 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -464,6 +464,9 @@
 extern const char kMojoLoadingName[];
 extern const char kMojoLoadingDescription[];
 
+extern const char kModuleScriptsName[];
+extern const char kModuleScriptsDescription[];
+
 extern const char kNewAudioRenderingMixingStrategyName[];
 extern const char kNewAudioRenderingMixingStrategyDescription[];