TaskManager: when shown or activated, select the last active tab.

chrome/browser/task_management/task_manager_interface.h

Index: chrome/browser/task_management/task_manager_interface.h
diff --git a/chrome/browser/task_management/task_manager_interface.h b/chrome/browser/task_management/task_manager_interface.h
index e021bd6f7bfb0092a6fe09ea8366bf37ba3e0f5e..9b62f0ba7aad3005e412f43cab816baaa239c3c1 100644
--- a/chrome/browser/task_management/task_manager_interface.h
+++ b/chrome/browser/task_management/task_manager_interface.h
@@ -24,6 +24,10 @@
 
 class PrefRegistrySimple;
 
+namespace content {
+class WebContents;
+}  // namespace content
+
 namespace net {
 class URLRequest;
 }  // namespace net
@@ -205,6 +209,12 @@ class TaskManagerInterface {
   // the Task with |task_id| is running.
   virtual size_t GetNumberOfTasksOnSameProcess(TaskId task_id) const = 0;
 
+  // Returns the TaskId associated with the main task for |web_contents|.
+  // Returns -1 if |web_contents| is nullptr or does not currently have an
+  // associated Task.
+  virtual TaskId GetTaskIdForWebContents(
+      content::WebContents* web_contents) const = 0;
+
   // Returns true if the resource |type| usage calculation is enabled and
   // the implementation should refresh its value (this means that at least one
   // of the observers require this value). False otherwise.