WebUI TaskManager: Add "Activate page" feature.

chrome/browser/task_manager/task_manager.cc

Index: chrome/browser/task_manager/task_manager.cc
diff --git a/chrome/browser/task_manager/task_manager.cc b/chrome/browser/task_manager/task_manager.cc
index fd359387adbee577938af616371525bc858a1c73..914e3f03115a2ef8446fa585306b3520f3fc2fc6 100644
--- a/chrome/browser/task_manager/task_manager.cc
+++ b/chrome/browser/task_manager/task_manager.cc
@@ -566,6 +566,11 @@ bool TaskManagerModel::GetV8Memory(int index, size_t* result) const {
   return true;
 }
 
+bool TaskManagerModel::CanActivate(int index) const {
+  CHECK_LT(index, ResourceCount());
+  return GetResourceTabContents(index) != NULL;
+}
+
 bool TaskManagerModel::CanInspect(int index) const {
   CHECK_LT(index, ResourceCount());
   return resources_[index]->CanInspect();