Re-expose webrender debugger feature in components/servo

Update ws in debugger  to 0.7.3

Update lockfile

components/debugger/Cargo.toml

@@ -12,4 +12,4 @@ crate_type = ["rlib"]
 
 [dependencies]
 log = "0.3.5"
-ws = "0.6"
+ws = "0.7.3"

components/servo/Cargo.toml

@@ -17,6 +17,7 @@ webdriver = ["webdriver_server"]
 energy-profiling = ["profile_traits/energy-profiling"]
 debugmozjs = ["script/debugmozjs"]
 googlevr = ["webvr/googlevr"]
+webrender_debugger = ["webrender/debugger"]
 oculusvr = ["webvr/oculusvr"]
 unstable = [
     "euclid/unstable",