Add --enable-html-imports commandline switch and about-flags entry.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index fe4150eab0cd4dc80dca42a04aa4fb6b673d9aa3..47c72f7cccd1184abfcca63cdc9daf7b5b70a052 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -246,6 +246,9 @@ const char kDisableWebSecurity[]            = "disable-web-security";
 // Enable an experimental WebSocket implementation.
 const char kEnableExperimentalWebSocket[] = "enable-experimental-websocket";
 
+// Enable HTML Imports
+extern const char kEnableHTMLImports[] = "enable-html-imports";
+
 // Disables WebKit's XSSAuditor. The XSSAuditor mitigates reflective XSS.
 const char kDisableXSSAuditor[]             = "disable-xss-auditor";