Fix typo in WebViewImpl::updatePageDefinedViewportConstraints

Looks like you wanted to compare height to height, not height to width.

BUG=None
TESTS=WebFrameTest in webkit_unit_tests

Review URL: https://codereview.chromium.org/173823002

git-svn-id: svn://svn.chromium.org/blink/trunk@167533 bbb929c8-8fbe-4397-9dbb-9b2b20218538