Upgrade SVGTextLayoutEngine's dumpTextBoxes() to use String::substring

In debugging crbug.com/264211 I found dumpTextBoxes no longer compiles
with DUMP_TEXT_FRAGMENTS=1 because it uses outdated technology based
on bloated characters. This patch upgrades dumpTextBoxes to compile
with the new String function.

BUG=264211

Review URL: https://chromiumcodereview.appspot.com/21145006

git-svn-id: svn://svn.chromium.org/blink/trunk@155154 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Change many callers of updateStyleIfNeeded() to updateStyleForNodeIfNeeded()

Many callers of updateStyleIfNeeded() just need to update the style of the node
they're currently operating on (and its ancestors) and don't need to update the
style of the whole document. We can replace these calls with updateStyleForNodeIfNeeded.

There are a few other places that look like they could use this (ex. accessibility) but
I only changed ones I was confident were safe.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/21152004

git-svn-id: svn://svn.chromium.org/blink/trunk@155155 bbb929c8-8fbe-4397-9dbb-9b2b20218538