Deflake Bbr2DefaultTopologyTest.BandwidthIncreaseBB2UAggregation.

This test increases the bandwidth mid-test by 100 times and expect BBR2 can discover at least 18% of the new bandwidth at the end of the test. This change reduces it  to 15%.

PiperOrigin-RevId: 502662086
diff --git a/quiche/quic/core/congestion_control/bbr2_simulator_test.cc b/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
index ce9e44c..f08805f 100644
--- a/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
@@ -1345,9 +1345,9 @@
       [this]() { return sender_endpoint_.bytes_to_transfer() == 0; },
       QuicTime::Delta::FromSeconds(50));
   EXPECT_TRUE(simulator_result);
-  // Ensure at least 30% of the full bandwidth is observed.
+  // Ensure at least 15% of the full bandwidth is observed.
   EXPECT_APPROX_EQ(params.test_link.bandwidth,
-                   sender_->ExportDebugState().bandwidth_hi, 0.82f);
+                   sender_->ExportDebugState().bandwidth_hi, 0.85f);
 }
 
 // Test Bbr2's reaction to a 100x bandwidth increase during a transfer with BB2U
@@ -1387,9 +1387,9 @@
       [this]() { return sender_endpoint_.bytes_to_transfer() == 0; },
       QuicTime::Delta::FromSeconds(50));
   EXPECT_TRUE(simulator_result);
-  // Ensure at least 20% of the full bandwidth is observed.
+  // Ensure at least 15% of the full bandwidth is observed.
   EXPECT_APPROX_EQ(params.test_link.bandwidth,
-                   sender_->ExportDebugState().bandwidth_hi, 0.82f);
+                   sender_->ExportDebugState().bandwidth_hi, 0.85f);
 }
 
 // Test the number of losses incurred by the startup phase in a situation when