Pass correct client coordinates for mouse events synthesized from a GestureTap

LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html

Index: LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html
diff --git a/LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html b/LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html
index 90b80d3ad44684aabc31b818a9fbeb504a062937..40594b117f3cdbf80b9b2b1fc0b93d5ddc4756fa 100644
--- a/LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html
+++ b/LayoutTests/fast/events/touch/gesture/gesture-tap-frame-scrolled.html
@@ -16,11 +16,12 @@ body {
 <div id=console></div>
 <script>
 var event;
-window.scrollTo(0, 3);
+var scrollOffset = 3;

[Rick Byers, 2014/10/10 00:39:35]

nit: call this windowScrollOffset (to avoid confusion with the frame scroll
offset).

+window.scrollTo(0, scrollOffset);
 var rect = target.getBoundingClientRect();
 var point = {
     x: rect.left + rect.width / 2,
-    y: rect.top + rect.height / 2 - 3
+    y: rect.top + rect.height / 2
 };
 
 var eventReceived = {};
@@ -31,8 +32,8 @@ function onEventInFrame(e) {
     eventReceived[e.type] = true;
     shouldBe("event.screenX", "point.x");
     shouldBe("event.screenY", "point.y");
-    shouldBe("event.clientX", "50 / 2");
-    shouldBe("event.clientY", "50 / 2 + 7");

[Rick Byers, 2014/10/10 00:39:35]

Ok so it looks like the real problem here is that I was thinking pageY when I
typed clientY - damn.  To help avoid this sort of bug in the future, can you
please also check the pageX/pageY co-ordinates here too?  I.e. you'll need to
actually use the 7 value (maybe call it frameScrollOffset) somewhere (eg. to
verify that the test properly cased the frame to scroll in the first place at
all)...

+    shouldBe("event.clientX", "point.x");

[Rick Byers, 2014/10/10 00:39:35]

using "point" here seems wrong because point is in window co-ordinate space but
client is in the co-ordinate space of the frame.  We're apparently getting away
with it only because the frame happens to be at (0,0) in the document.

Can you fix this by adding some margin to the target, then change the
expectation to be just the relative co-ordinate.  Eg. maybe:

var pointInFrame = {
  x: rect.width / 2,
  y: rect.height / 2
};
var pointInWindow = {
  x: rect.left + pointInFrame.x,
  y: rect.top + pointInFrame.y
};

[Zeeshan Qureshi, 2014/10/10 00:47:23]

That looks more readable, will update.

+    shouldBe("event.clientY", "point.y + scrollOffset");
 }
 
 description("Verifies that a tap occuring in a scrolled iframe has the correct co-ordinates");