Make text input relayout when value is changed directly.

[glennw]

No description provided.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/4333

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[glennw]

r? @Ms2ger or @jdm

[frewsxcv]

I'm new to the codebase, so ignore me if it's not necessary, but it might be nice if there were code comments briefly describing why the force relayout is necessary

[jdm]

r+

[jdm]

@frewsxcv: I filed #5329 about that; I think it will be better to do it all at once.

[bors-servo]

saw approval from jdm
at glennw@0db6f85

[bors-servo]

merging glennw/servo/input-relayout = 0db6f85 into auto

[bors-servo]

glennw/servo/input-relayout = 0db6f85 merged ok, testing candidate = b7e66c5

[bors-servo]

all tests pass:
success: http://build.servo.org/builders/linux1/builds/1121
success: http://build.servo.org/builders/linux2/builds/1121
success: http://build.servo.org/builders/android/builds/1155
success: http://build.servo.org/builders/mac1/builds/1334
success: http://build.servo.org/builders/mac2/builds/1337
success: http://build.servo.org/builders/gonk/builds/303

[bors-servo]

fast-forwarding master to auto = b7e66c5