Update RateStatistics to handle too-little-data case.

webrtc/common_video/bitrate_adjuster_unittest.cc

Index: webrtc/common_video/bitrate_adjuster_unittest.cc
diff --git a/webrtc/common_video/bitrate_adjuster_unittest.cc b/webrtc/common_video/bitrate_adjuster_unittest.cc
index 23b278731ef4665ce793d333d8dd23d434fab558..d0517e4fcb368c487d1c4179d1b2e785c3254c6c 100644
--- a/webrtc/common_video/bitrate_adjuster_unittest.cc
+++ b/webrtc/common_video/bitrate_adjuster_unittest.cc
@@ -48,7 +48,8 @@ class BitrateAdjusterTest : public ::testing::Test {
     // target bitrate within clamp.
     uint32_t target_bitrate_bps = adjuster_.GetTargetBitrateBps();
     uint32_t adjusted_bitrate_bps = adjuster_.GetAdjustedBitrateBps();
-    uint32_t estimated_bitrate_bps = adjuster_.GetEstimatedBitrateBps();
+    uint32_t estimated_bitrate_bps =
+        adjuster_.GetEstimatedBitrateBps().value_or(target_bitrate_bps);
     uint32_t adjusted_lower_bound_bps =
         GetTargetBitrateBpsPct(kMinAdjustedBitratePct);
     uint32_t adjusted_upper_bound_bps =