Cursor-tracking in Android Chromoting client.

This is a first step towards implementing the new gestures:
* Single-finger swipe moves the cursor (and pans the image in the
opposite direction).
* Single-finger tap injects left-click.
* Two-finger tap injects right-click.
* Two-finger pinch to zoom (as before)
* Three-finger tap to show the action-bar (as before)

There are some regressions (to keep this CL simple) but I plan to
address these in follow-up CLs:

* No constraints on image-positioning or zoom-level.
* Cannot do left-button dragging.
* Cannot send middle-button press.
* Removed minimum-scroll constraint, as that makes it difficult to
control the cursor precisely.

BUG=270348

Review URL: https://codereview.chromium.org/26336004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231042 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231042
DevTools: Add URL query parameter to json/new command

TBR=pfeldman,bulach,mnaganov
BUG=311014

Review URL: https://codereview.chromium.org/39993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231043 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231043