Add null-check for LayoutTextControl::innerEditorElement()

Add a null-check in LayoutTextControl::computeIntrinsicLogicalWidths to
ensure that innerEditorElement is non-null before calling layoutBox().

BUG=623718
TBR=dgrogan@chromium.org

Review-Url: https://codereview.chromium.org/2155513002
Cr-Commit-Position: refs/heads/master@{#405661}
1 file changed