Adds function for activating a tab.

tools/telemetry/telemetry/browser_backend.py

Index: tools/telemetry/telemetry/browser_backend.py
diff --git a/tools/telemetry/telemetry/browser_backend.py b/tools/telemetry/telemetry/browser_backend.py
index 702f249d95d9cd2b202b6ecd36c566a2af3b495a..80b356408ce5532c2dd18858ca0fe1061ca17a81 100644
--- a/tools/telemetry/telemetry/browser_backend.py
+++ b/tools/telemetry/telemetry/browser_backend.py
@@ -43,6 +43,21 @@ class TabController(object):
     self._UpdateTabList()
     return url in self._tab_list
 
+  def ActivateTab(self, debugger_url, timeout=None):
+    """Activates a tab.
+

[nduca, 2012/12/21 22:15:23]

This doesn't make sense on the tab controller.

browser.tabs[2].Activate should be how this works.

[Danh Nguyen, 2012/12/26 19:13:04]

Done.

[Danh Nguyen, 2012/12/26 19:13:04]

Done.  I'm moving this function to tab.py as you suggested.

[dtu, 2012/12/27 18:57:25]

This is actually similar to how Close() works. tab.Close() calls
_tab_controller.CloseTab(), because TabController has a lot of the other logic
needed for CloseTab()

+    Args:
+      debugger_url: webSocketDebuggerUrl of the tab.
+    """
+    tab_id = debugger_url.split('/')[-1]
+    try:
+      response = self._browser_backend.Request('activate/%s' % tab_id,
+                                               timeout=timeout)
+    except urllib2.HTTPError:
+      raise Exception('Unable to activate tab, tab id not found: %s' % tab_id)
+    assert response == 'Target activated'
+    self._UpdateTabList()
+
   def CloseTab(self, debugger_url, timeout=None):
     # TODO(dtu): crbug.com/160946, allow closing the last tab on some platforms.
     # For now, just create a new tab before closing the last tab.