Merge "Fix linkage when building with clang, Intel CC or gcc -O0"

namespace android {

// static

const int64_t WifiDisplaySource::kReaperIntervalUs;

const int64_t WifiDisplaySource::kTeardownTriggerTimeouSecs;

const int64_t WifiDisplaySource::kPlaybackSessionTimeoutSecs;

const int64_t WifiDisplaySource::kPlaybackSessionTimeoutUs;

const AString WifiDisplaySource::sUserAgent = MakeUserAgent();

WifiDisplaySource::WifiDisplaySource(