Prevent TouchEvent Crash on X
When TouchEvents are copied the base::NativeEvent of the copy is set as null for
GenericEvent types, such as touchs.
Touch Release and Cancel events are set to remove a native touch id mapping upon
destruction.
This causes copied Touch Release/Cancel events to attempt to remove a mapping on
a null native event. Leading to a crash.
I've explicitly defined a copy constructor on TouchEvent to stop copied events
from attempting to remove this mapping.
TEST=EventsXTest.CopiedTouchEventNotRemovingFromNativeMapping
BUG=467102
Review URL: https://codereview.chromium.org/
1026573002
Cr-Commit-Position: refs/heads/master@{#321563}