vea_unittest: Set longer flush timeout.

Originally we assume the FPS of all encoders should be larger than the
minimum FPS 30. But the FPS for multiple encoder test case should be
divided by the number of the encoders. This CL changes the timeout to
2 seconds assuming the FPS should be at least larger than 5.

Bug: chromium:820313
Test: Pass video_encode_accelerator_unittest with 1920x1080 video at
      scarlet device

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ic91a6aa8b00ee0bdb73da407e4c435ea2979a2c4
Reviewed-on: https://chromium-review.googlesource.com/997253Reviewed-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Chih-Yu Huang <akahuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549404}

media/gpu/video_encode_accelerator_unittest.cc

@@ -100,10 +100,11 @@ const uint32_t kMinPerfFPS = 30;
 const unsigned int kMinFramesForBitrateTests = 300;
 // The percentiles to measure for encode latency.
 const unsigned int kLoggedLatencyPercentiles[] = {50, 75, 95};
-// Timeout for the flush is completed. The default FPS is 30, so the processing
-// time for 1 frame is about 33 milliseconds. Here we set 10x period of time
-// considering that there might be some pending frames.
-const unsigned int kFlushTimeoutMs = 300;
+// Timeout for the flush is completed. In the multiple encoder test case, the
+// FPS might be lower than expected. Let us assume that the lowest FPS is 5,
+// then the period per frame is 200 milliseconds. Here we set the timeout 10x
+// periods considering that there might be some pending frames.
+const unsigned int kFlushTimeoutMs = 2000;
 
 // The syntax of multiple test streams is:
 //  test-stream1;test-stream2;test-stream3