DevTools: Fix Ctrl-Z for source color picker

All changes to the color text from the spectrum should count as one change
for undo/redo. Pressing Ctrl-Z should also move the cursor to the change.

R=lushnikov

Review-Url: https://codereview.chromium.org/2168713004
Cr-Commit-Position: refs/heads/master@{#407054}
2 files changed