Migrate DevToolsHTTPHandlerImpl to using DevToolsTargetImpl

TEST=tools/perf/run_benchmark page_cycler.intl_ja_zh --page-filter=google
BUG=None

Review URL: https://codereview.chromium.org/48033003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231363 0039d316-1c4b-4281-b951-d872f2087c98
MAD out of instant.

NOTRY=true
BUG=None

Review URL: https://codereview.chromium.org/49043005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231364 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231364