Make NGInlineNode::ShapeText() not to reuse ShapeResult for letter-spacing

This patch changes |NGInlineNode::ShapeText()| not to reuse
|ShapeResult| for text with CSS property "letter-spacing" because we
modify |ShapeResult| directly to apply letter spacing. Thus, letter-
spacing is applied more than once on reused portion of |ShapeResult|.

Note: This patch also changes number of bits of
|SharepResult::num_glyphs_| from 30 to 29 to hold bit flags in
|unsigned| (32-bit) for re-landing[1].

[1] http://crrev.com/c/2390615 Revert "Make NGInlineNode::ShapeText()
not to reuse ShapeResult for letter-spacing"

Bug: 1124446
Change-Id: I120cc379a191e1499ac1548a569474ed03d0f6a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391890
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804185}