Correct the (x, y) position of dragstart event initiated by touch event

Correct the position of dragstart event

This patch is to fix an issue that the x and y position of dragstart event
is not correct if it is triggered by long press event.

BUG=None
TEST=fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=150809

[Hongbo Min, 2013-05-17 01:14:32]

varunjain@, please have a review. Thanks.

[varunjain, 2013-05-17 16:43:50]

+hayato & dglazkov who have reviewed changes in this code before as I am not a
reviewer.

https://codereview.chromium.org/14598021/diff/1/Source/core/page/EventHandler...
File Source/core/page/EventHandler.cpp (right):

https://codereview.chromium.org/14598021/diff/1/Source/core/page/EventHandler...
Source/core/page/EventHandler.cpp:2413: m_mouseDown = mouseDragEvent;
I think this change is correct. But I am a little worried that we are assigning
a drag event to m_mouseDown. I think the field should be re-named to
m_dragSrcReferenceMouseEvent or something like that, because thats basically
what it is being used for, i.e. as a reference to construct the drag start event
sent in EventHandler::handleDrag()

[Hongbo Min, 2013-05-20 01:47:15]

https://codereview.chromium.org/14598021/diff/1/Source/core/page/EventHandler...
File Source/core/page/EventHandler.cpp (right):

https://codereview.chromium.org/14598021/diff/1/Source/core/page/EventHandler...
Source/core/page/EventHandler.cpp:2413: m_mouseDown = mouseDragEvent;
On 2013/05/17 16:43:51, varunjain wrote:
> I think this change is correct. But I am a little worried that we are
assigning
> a drag event to m_mouseDown. I think the field should be re-named to
> m_dragSrcReferenceMouseEvent or something like that, because thats basically
> what it is being used for, i.e. as a reference to construct the drag start
event
> sent in EventHandler::handleDrag()

I don't rename m_mouseDown field since it just records the mouse down event
triggered by pressing mouse button or long press gesture. You may notice the
m_mouseDown field is assigned in handleMousePressEvent and referenced by
handleDrag to dispatch drag event. 

Instead, I create a specific PlatformMouseEvent with MousePressed event type and
assign it m_mouseDown, by this way, it could avoid the potential side effect
caused by incorrect event type defined in mouseDragEvent for m_mouseDown field.

Does it make more sense now?

[hayato, 2013-05-20 08:12:31]

lgtm

Note that I had difficult time to understand how m_mouseDown will be used later
after it's assigned. There seems a lot of hidden assumptions when m_mouseDown
should be assigned and when it should be used.

I guess this is not this patch's fault.

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
File
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html
(right):

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html:29:
}
Could you add a semicolon at the end of line?

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html:30:
document.onmousedown = function() {
document.getElementById("mouseDownResult").innerHTML = "FAIL"; }
Ditto.

[Hongbo Min, 2013-05-20 09:21:25]

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
File
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html
(right):

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html:29:
}
On 2013/05/20 08:12:31, hayato wrote:
> Could you add a semicolon at the end of line?

Done.

But I am wondering that is it enforced by JS coding style?

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html:30:
document.onmousedown = function() {
document.getElementById("mouseDownResult").innerHTML = "FAIL"; }
On 2013/05/20 08:12:31, hayato wrote:
> Ditto.

Done.

[commit-bot: I haz the power, 2013-05-20 09:27:31]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hongbo.min@intel.com/14598021/15001

[hayato, 2013-05-20 09:28:15]

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
File
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html
(right):

https://codereview.chromium.org/14598021/diff/9001/LayoutTests/fast/events/to...
LayoutTests/fast/events/touch/gesture/long-press-on-draggable-element-triggers-drag.html:29:
}
On 2013/05/20 09:21:26, Hongbo Min wrote:
> On 2013/05/20 08:12:31, hayato wrote:
> > Could you add a semicolon at the end of line?
> 
> Done.
> 
> But I am wondering that is it enforced by JS coding style?

Thank you. I don't know whether there is a coding style for that in blink, but
it's preferable in general in JS.

[Hongbo Min, 2013-05-20 09:34:12]

hayato@, could you please help add the OWNER of EventHandler.cpp to review
futher for commit? I have no idea about who is expertized at it via OWNERS file.
Thanks.

[commit-bot: I haz the power, 2013-05-20 09:39:15]

Retried try job too often on blink_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=blink_pres...

[hayato, 2013-05-20 09:49:01]

On 2013/05/20 09:34:12, Hongbo Min wrote:
> hayato@, could you please help add the OWNER of EventHandler.cpp to review
> futher for commit? I have no idea about who is expertized at it via OWNERS
file.
> Thanks.

I asked nominating me as an OWNER of Source/core on last Friday.
Hopefully, I'll lgtm to the change of EventHander.cpp as an OWNER next time. :)

[dglazkov, 2013-05-21 16:52:32]

LGTM.

[commit-bot: I haz the power, 2013-05-21 16:56:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hongbo.min@intel.com/14598021/15001

[commit-bot: I haz the power, 2013-05-21 17:43:09]

Change committed as 150809