Telemetry: Clean up tap and click_element gestures.

The tap and click_element page actions have a very similar purpose but use a very
different implementation. This patch renames click_element to javascript_click
to indicate that it is not using synthetic gestures as tap does. It also replaces
click_element with tap inside smoothness measurements, so we exercise the entire
input stack. In other places we keep click_element (now javascript_click) because
tap's functionality isn't always sufficient (click elements outside of the view;
clicking on very small elements causes Chrome to magnify the element first).
Further, tap now supports all ways to select an element that click_element
supported (by text, xpath etc).

This CL also removes the tap_element page action, which was only used inside
smoothness for the pica page set. This case is currently broken and adamk@ said
he'd re-implement it using synthetic gestures if needed.

BUG=339233

Review URL: https://codereview.chromium.org/181483002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255355 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255355