Change rtc::TimeNanos and rtc::TimeMicros return value from uint64_t to int64_t.

webrtc/modules/video_capture/test/video_capture_unittest.cc

Index: webrtc/modules/video_capture/test/video_capture_unittest.cc
diff --git a/webrtc/modules/video_capture/test/video_capture_unittest.cc b/webrtc/modules/video_capture/test/video_capture_unittest.cc
index 0090006fea26434bbbea2732836d8dc9abeb82cf..0f9f0aea41604c04578890a78b99aa7285f889d7 100644
--- a/webrtc/modules/video_capture/test/video_capture_unittest.cc
+++ b/webrtc/modules/video_capture/test/video_capture_unittest.cc
@@ -472,8 +472,8 @@ TEST_F(VideoCaptureExternalTest, TestExternalCapture) {
 #define MAYBE_FrameRate FrameRate
 #endif
 TEST_F(VideoCaptureExternalTest, MAYBE_FrameRate) {
-  uint64_t testTime = 3 * rtc::kNumNanosecsPerSec;
-  uint64_t startTime = rtc::TimeNanos();
+  int64_t testTime = 3 * rtc::kNumNanosecsPerSec;
+  int64_t startTime = rtc::TimeNanos();
 
   while ((rtc::TimeNanos() - startTime) < testTime) {
     size_t length = webrtc::CalcBufferSize(webrtc::kI420,