DevTools: make paint profiler target-aware

Source/devtools/front_end/common/utilities.js

Index: Source/devtools/front_end/common/utilities.js
diff --git a/Source/devtools/front_end/common/utilities.js b/Source/devtools/front_end/common/utilities.js
index d38d236f832f5f32fda2a4a05fda22efaac753de..32d56cc2b87e085fd4e98071d1d20e6ac4c1adeb 100644
--- a/Source/devtools/front_end/common/utilities.js
+++ b/Source/devtools/front_end/common/utilities.js
@@ -1777,3 +1777,29 @@ CallbackBarrier.prototype = {
 function suppressUnused(value)
 {
 }
+
+/**
+ * @constructor
+ * @param {!T} targetObject
+ * @template T
+ */
+function WeakReference(targetObject)
+{
+    this._targetObject = targetObject;
+}
+
+WeakReference.prototype = {
+    /**
+     * @return {?T}
+     */
+    get: function()
+    {
+        return this._targetObject;
+    },
+
+    clear: function()
+    {
+        this._targetObject = null;
+    }
+};
+