Send position with mouse up/down events

Send position with mouse up/down events. 

This change ensures that client & host agree on the position of mouse button events. This is especially relevant in the case where the client's plugin is not receiving mouse move events because it doesn't have focus, and the user clicks on the plugin. Without positional information, the host will process the button event at the host's initial mouse position, very likely not at the position intended by the user. 

BUG=110688
TEST=manual

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=119934

[garykac, 2012-01-31 01:27:57]

LGTM

[Wez, 2012-01-31 01:28:47]

LGTM, but please update the CL description to summarise why we need this, and
remove the empty TEST= line.

[Wez, 2012-01-31 01:29:18]

On 2012/01/31 01:28:47, Wez wrote:
> LGTM, but please update the CL description to summarise why we need this, and
> remove the empty TEST= line.

Sorry, ignore the bit about the TEST= line, which is verifiably not empty...

[garykac, 2012-01-31 01:33:25]

(and run it through the trybots)

[commit-bot: I haz the power, 2012-01-31 17:43:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dcaiafa@chromium.org/9264060/1

[commit-bot: I haz the power, 2012-01-31 19:33:37]

Change committed as 119934