Add FeatureList instance to renderers and propgate enable/disable flags.

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 b227056e5c5a702efa60e6a2e248f2c12fbafe98..1ce0a4c47506749d262c969c091db51488e600f0 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -104,6 +104,9 @@ const char kDisableDomainBlockingFor3DAPIs[] =
 // Disable experimental WebGL support.
 const char kDisableExperimentalWebGL[]      = "disable-webgl";
 
+// Comma-separated list of feature names to disable. See also kEnableFeatures.
+const char kDisableFeatures[]               = "disable-features";
+
 // Disable FileSystem API.
 const char kDisableFileSystem[]             = "disable-file-system";
 
@@ -344,6 +347,9 @@ const char kEnableExperimentalCanvasFeatures[] =
 const char kEnableExperimentalWebPlatformFeatures[] =
     "enable-experimental-web-platform-features";
 
+// Comma-separated list of feature names to enable. See also kDisableFeatures.
+const char kEnableFeatures[] = "enable-features";
+
 // Enable Web Bluetooth.
 const char kEnableWebBluetooth[] = "enable-web-bluetooth";