Bug 1345119 - Part 2: Server side for retrieving offset parent of DOM node. r=pbro

MozReview-Commit-ID: I51NHlxv6Mp

devtools/server/actors/inspector.js

@@ -2647,6 +2647,22 @@ var WalkerActor = protocol.ActorClassWithSpec(walkerSpec, {
 
     return this.layoutActor;
   },
+
+  /**
+   * Get the offset parent of the node
+   * If the offset parent is statically positioned, there is no offset parent
+   * and null is returned.
+   * Returns the DOMNode for the offset parent if it exists
+   */
+  getOffsetParent: function (domnode) {
+    let offsetParent = domnode.rawNode.offsetParent;
+
+    if (!offsetParent || CssLogic.getComputedStyle(offsetParent).position === "static") {
+      return null;
+    }
+
+    return this._ref(offsetParent);
+  },
 });
 
 /**

devtools/shared/specs/inspector.js

@@ -374,7 +374,15 @@ const walkerSpec = generateActorSpec({
       response: {
         actor: RetVal("layout")
       }
-    }
+    },
+    getOffsetParent: {
+      request: {
+        node: Arg(0, "domnode")
+      },
+      response: {
+        node: RetVal("nullable:domnode")
+      }
+    },
   }
 });