Filter out vsync events from HWC with duplicate timestamps

void HWComposer::vsync(int disp, int64_t timestamp) {

    if (uint32_t(disp) < HWC_NUM_PHYSICAL_DISPLAY_TYPES) {

        {

            Mutex::Autolock _l(mLock);

            // There have been reports of HWCs that signal several vsync events

            // with the same timestamp when turning the display off and on. This

            // is a bug in the HWC implementation, but filter the extra events

            // out here so they don't cause havoc downstream.

            if (timestamp == mLastHwVSync[disp]) {

                ALOGW("Ignoring duplicate VSYNC event from HWC (t=%lld)",

                        timestamp);

                return;

            }

            mLastHwVSync[disp] = timestamp;

        }

        char tag[16];

        snprintf(tag, sizeof(tag), "HW_VSYNC_%1u", disp);

        ATRACE_INT(tag, ++mVSyncCounts[disp] & 1);

        mEventHandler.onVSyncReceived(disp, timestamp);

        Mutex::Autolock _l(mLock);

        mLastHwVSync[disp] = timestamp;

    }

}