Remove references to WebTouchEvent.changedTouches

Remove references to WebTouchEvent.changedTouches

Now that Blink fully populates the |WebTouchEvent.touches| field when
offering events to plugins, we can safely stop using
|WebTouchEvent.changedTouches|.

This is part 3 of a 4-sided patch simplifying WebTouchEvent:
1) https://codereview.chromium.org/557863002/
2) https://codereview.chromium.org/558773002/
3) This change
4) https://codereview.chromium.org/560493003/

BUG=358132
Committed: https://crrev.com/dc5b3dc2a1481fa05fbfb4c38a7cff1e6af1454f
Cr-Commit-Position: refs/heads/master@{#294390}

[jdduke (slow), 2014-09-10 00:55:24]

jdduke@chromium.org changed reviewers:
+ fsamuel@chromium.org

[jdduke (slow), 2014-09-10 00:55:25]

fsamuel@: Owner review for content/renderer/browser_plugin/browser_plugin.cc?
Sorry for the noise, but this change must be separate from the patch you
reviewed previously (https://codereview.chromium.org/557863002/), as we need to
first tweak how Blink synthesizes the event. Thanks.

[Fady Samuel, 2014-09-10 01:10:54]

https://codereview.chromium.org/559693003/diff/1/content/renderer/browser_plu...
File content/renderer/browser_plugin/browser_plugin.cc (right):

https://codereview.chromium.org/559693003/diff/1/content/renderer/browser_plu...
content/renderer/browser_plugin/browser_plugin.cc:580: const
blink::WebInputEvent* modified_event = &event;
We can probably get rid of this local variable too.

[jdduke (slow), 2014-09-10 15:31:23]

https://codereview.chromium.org/559693003/diff/1/content/renderer/browser_plu...
File content/renderer/browser_plugin/browser_plugin.cc (right):

https://codereview.chromium.org/559693003/diff/1/content/renderer/browser_plu...
content/renderer/browser_plugin/browser_plugin.cc:580: const
blink::WebInputEvent* modified_event = &event;
On 2014/09/10 01:10:54, Fady Samuel wrote:
> We can probably get rid of this local variable too.

Good catch, for whatever reason I thought keyboard events might have been
modified. Done.

[Fady Samuel, 2014-09-10 15:32:51]

lgtm! I love it when code gets simpler to read and understand! :D

[jdduke (slow), 2014-09-11 14:00:19]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-09-11 14:00:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/559693003/20001

[commit-bot: I haz the power, 2014-09-11 15:14:58]

Committed patchset #2 (id:20001) as f96fedffdee970d2de5b8cc16da59529a0ec9008

[commit-bot: I haz the power, 2014-09-11 15:19:21]

Patchset 2 (id:??) landed as
https://crrev.com/dc5b3dc2a1481fa05fbfb4c38a7cff1e6af1454f
Cr-Commit-Position: refs/heads/master@{#294390}