DevTools: Make GC button in timeline to fire gc events in all targets

BUG=

Review URL: https://codereview.chromium.org/457523004

git-svn-id: svn://svn.chromium.org/blink/trunk@180148 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js

@@ -720,7 +720,9 @@ WebInspector.TimelinePanel.prototype = {
 
     _garbageCollectButtonClicked: function()
     {
-        HeapProfilerAgent.collectGarbage();
+        var targets = WebInspector.targetManager.targets();
+        for (var i = 0; i < targets.length; ++i)
+            targets[i].heapProfilerAgent().collectGarbage();
     },
 
     _onClearButtonClick: function()