Move ResourceFetchTiming into Arc

The purpose of this commit is to ensure that the Response object has
access to Timing updates as previously the Response object simply
stored a ResourceFetchTiming struct so updates on ResourceFetchTiming
that were not explicitly done on the Response would not be passed down.
The references to ServoArc are added because Response uses
servo_arc::Arc rather than std::sync::Arc as is used elsewhere. So,
we've switched those other places to servo_arc::Arc instead of switching
Response to std::sync::Arc.

components/net_traits/response.rs

@@ -114,7 +114,8 @@ pub struct Response {
     #[ignore_malloc_size_of = "AtomicBool heap size undefined"]
     pub aborted: Arc<AtomicBool>,
     /// track network metrics
-    pub resource_timing: ResourceFetchTiming,
+    #[ignore_malloc_size_of = "Mutex heap size undefined"]
+    pub resource_timing: Arc<Mutex<ResourceFetchTiming>>,
 }
 
 impl Response {
@@ -137,7 +138,7 @@ impl Response {
             internal_response: None,
             return_internal: true,
             aborted: Arc::new(AtomicBool::new(false)),
-            resource_timing: resource_timing,
+            resource_timing: Arc::new(Mutex::new(resource_timing)),
         }
     }
 
@@ -171,7 +172,9 @@ impl Response {
             internal_response: None,
             return_internal: true,
             aborted: Arc::new(AtomicBool::new(false)),
-            resource_timing: ResourceFetchTiming::new(ResourceTimingType::Error),
+            resource_timing: Arc::new(Mutex::new(ResourceFetchTiming::new(
+                ResourceTimingType::Error,
+            ))),
         }
     }
 
@@ -217,8 +220,8 @@ impl Response {
         }
     }
 
-    pub fn get_resource_timing(&self) -> &ResourceFetchTiming {
-        &self.resource_timing
+    pub fn get_resource_timing(&self) -> Arc<Mutex<ResourceFetchTiming>> {
+        Arc::clone(&self.resource_timing)
     }
 
     /// Convert to a filtered response, of type `filter_type`.