[Panels] Fix crash when killing panel extension from TaskManager.

chrome/browser/task_manager/task_manager_resource_providers.cc

Index: chrome/browser/task_manager/task_manager_resource_providers.cc
diff --git a/chrome/browser/task_manager/task_manager_resource_providers.cc b/chrome/browser/task_manager/task_manager_resource_providers.cc
index 4f0121b588cdd723e741307bbad78fe8e2780ad2..a12f24e9ba9ef32ded5ba49e8172d5f33cecb8b2 100644
--- a/chrome/browser/task_manager/task_manager_resource_providers.cc
+++ b/chrome/browser/task_manager/task_manager_resource_providers.cc
@@ -712,7 +712,8 @@ void TaskManagerPanelResourceProvider::Observe(int type,
       for (PanelResourceMap::iterator iter = resources_.begin();
            iter != resources_.end(); ++iter) {
         Panel* panel = iter->first;
-        if (!panel->GetWebContents()) {
+        WebContents* panel_contents = panel->GetWebContents();
+        if (!panel_contents || panel_contents == web_contents) {
           Remove(panel);
           break;
         }