[Contextual Search] Change "Now on Tap" to "Contextual Cards"

BUG=644934

Review-Url: https://codereview.chromium.org/2361163003
Cr-Commit-Position: refs/heads/master@{#420899}
bool ContextualSearchFieldTrial::HasSwitch(const std::string& name) {
  return base::CommandLine::ForCurrentProcess()->HasSwitch(name);
}

bool ContextualSearchFieldTrial::HasSwitch(const std::string& name) {
  return base::CommandLine::ForCurrentProcess()->HasSwitch(name);
}
