Change about flag for doc.write to a tri-state so it can be disabled.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 8f6359952523df340f6b8859c4f04c4aee177104..d6d5a76846f255f7543dfb26fc023abb04a6d419 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1675,9 +1675,11 @@ const FeatureEntry kFeatureEntries[] = {
      // NOTE: if we want to add additional experiment entries for other
      // features controlled by kBlinkSettings, we'll need to add logic to
      // merge the flag values.
-     SINGLE_VALUE_TYPE_AND_VALUE(
+     ENABLE_DISABLE_VALUE_TYPE_AND_VALUE(
+         switches::kBlinkSettings,
+         "disallowFetchForDocWrittenScriptsInMainFrame=true",
          switches::kBlinkSettings,
-         "disallowFetchForDocWrittenScriptsInMainFrame=true")},
+         "disallowFetchForDocWrittenScriptsInMainFrame=false")},
 #if defined(OS_ANDROID)
     {"enable-ntp-popular-sites", IDS_FLAGS_NTP_POPULAR_SITES_NAME,
      IDS_FLAGS_NTP_POPULAR_SITES_DESCRIPTION, kOsAndroid,