Merge pull request #6 from skyostil/master

Import adb_profile_chrome.py from upstream Chromium
Fix pexpect import path

Fix the pexpect import path so that the script works even if there is no
system-level pexpect library installed.
Merge to upstream r252323

Merge adb_profile_chrome.py with upstream revision 252323. Note that
html file output is disabled pending an upstream refactoring.
Merge to upstream r253826

HTML output is now the default. Added third_party/trace-viewer submodule
to support this.
Updated the documentation to match the current functionality.