commit 3d7d1c4f000b6a955ca23a17aa1bee48e8c281b3
author abarth@chromium.org <abarth@chromium.org@bbb929c8-8fbe-4397-9dbb-9b2b20218538> Thu Jun 13 21:19:38 2013
committer abarth@chromium.org <abarth@chromium.org@bbb929c8-8fbe-4397-9dbb-9b2b20218538> Thu Jun 13 21:19:38 2013
tree 9197c126b27b1a8b842804902f76abfc1421f1e3
parent 57771439806f7c6e6a272efb1ea72900f5f6a015

XMLHttpRequest#responseText should use a rope

Instead of building a flat WTF::String from XMLHttpRequest response data, we
should build a v8::String rope. That way when web sites query the responseText
field repeatedly, every query will share the same underlying data.

This CL causes StringImpl::hashSlowCase to drop way down the CPU profile of
reloading Mobile Gmail:

Before: 1.08%  content_shell  content_shell          [.] WTF::StringImpl::hashSlowCase() const
After:  0.37%  content_shell  content_shell          [.] WTF::StringImpl::hashSlowCase() const

There are likely other savings as well, but the effect on StringImpl::hashSlowCase
is the most dramatic change to the profile.

R=jamesr

Review URL: https://chromiumcodereview.appspot.com/16925002

git-svn-id: svn://svn.chromium.org/blink/trunk@152380 bbb929c8-8fbe-4397-9dbb-9b2b20218538