Adds per-provider information to omnibox UMA logs.

Adds a fairly general structure to omnibox logs that can be used to pass information (that's not per-result information) from providers to the UMA logs.  Right now it's only used to pass whether the asynchronous pass of a provider has finished, but it will probably be used for other things in the future.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10380007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@137288 0039d316-1c4b-4281-b951-d872f2087c98
AutocompleteController::~AutocompleteController() {
  result_.Reset();  // Not really necessary.
  Stop(false);

  for (ACProviders::iterator i(providers_.begin()); i != providers_.end(); ++i)
    (*i)->Release();

  providers_.clear();  // Not really necessary.
}

AutocompleteController::~AutocompleteController() {
  result_.Reset();  // Not really necessary.
  Stop(false);

  for (ACProviders::iterator i(providers_.begin()); i != providers_.end(); ++i)
    (*i)->Release();

  providers_.clear();  // Not really necessary.
}
