[JSON Modules] Allow JSON Modules in ServiceWorker

-Allows mime type to be referenced from service worker installed scripts manager
-Introduces JSON modules as a feature flag so that the flag is accessible to the browser process
-Introduces service worker WPT tests for JSON Modules

This PR inspired the following change:
https://chromium-review.googlesource.com/c/chromium/src/+/1854504

Bug: 967018
Change-Id: I6939988ab0df3896bbd81dcd174312f871583574
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1825788
Reviewed-by: Kent Tamura <[email protected]>
Reviewed-by: Hiroki Nakagawa <[email protected]>
Reviewed-by: Hiroshige Hayashizaki <[email protected]>
Reviewed-by: Kouhei Ueno <[email protected]>
Commit-Queue: Sam Sebree <[email protected]>
Cr-Commit-Position: refs/heads/master@{#724516}
diff --git a/third_party/blink/common/features.cc b/third_party/blink/common/features.cc
index 1d51ad4..f445217 100644
--- a/third_party/blink/common/features.cc
+++ b/third_party/blink/common/features.cc
@@ -67,6 +67,9 @@
 const base::Feature kFastBorderRadius{"FastBorderRadius",
                                       base::FEATURE_ENABLED_BY_DEFAULT};
 
+const base::Feature kJSONModules{"JSONModules",
+                                 base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enable LayoutNG.
 const base::Feature kLayoutNG{"LayoutNG", base::FEATURE_ENABLED_BY_DEFAULT};