The D.C. Council has given a multimillion-dollar subsidy to a developer of the gentrifying H Street corridor. Without dissent, the council approved an emergency measure that grants a tax abatement to Steuart Investment Co., owner of the lot at the corner of Third and H Streets Northeast. The tax break is designed to help the Chevy Chase developer build a high-rise building with shopping, restaurants and apartments or condos. Under the law, Steuart’s property taxes will be frozen at what it paid in fiscal 2010 for 10 years. The company then will pay a portion of taxes above the fiscal 2010 level through fiscal 2030. The breaks are capped at $5 million — 7 percent of the project’s expected costs.