Platform dependent way of generating the seed for srand for simulations, so that they can be run in parallel.

The seed generated for Win won't be good enough to run the simulations in parallel.

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49829004

Cr-Commit-Position: refs/heads/master@{#9101}

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimators_test.cc

@@ -8,6 +8,11 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#ifndef WEBRTC_WIN
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
 #include <sstream>
 
 #include "webrtc/modules/remote_bitrate_estimator/include/remote_bitrate_estimator.h"
@@ -241,7 +246,14 @@ class BweFeedbackTest
   virtual ~BweFeedbackTest() {}
 
  protected:
-  void SetUp() override { BweTest::SetUp(); }
+  void SetUp() override {
+    unsigned int seed = Clock::GetRealTimeClock()->TimeInMicroseconds();
+#ifndef WEBRTC_WIN
+    seed *= getpid();
+#endif
+    srand(seed);
+    BweTest::SetUp();
+  }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BweFeedbackTest);
@@ -321,28 +333,27 @@ TEST_P(BweFeedbackTest, DISABLED_GoogleWifiTrace3Mbps) {
                filter.GetDelayStats(), std::vector<Stats<double>>());
 }
 
-TEST_P(BweFeedbackTest, PacedSelfFairnessTest) {
-  srand(Clock::GetRealTimeClock()->TimeInMicroseconds());
+TEST_P(BweFeedbackTest, PacedSelfFairness50msTest) {
+  RunFairnessTest(GetParam(), 4, 0, 300, 3000, 50);
+}
+
+TEST_P(BweFeedbackTest, PacedSelfFairness500msTest) {
   RunFairnessTest(GetParam(), 4, 0, 300, 3000, 50);
 }
 
 TEST_P(BweFeedbackTest, PacedSelfFairness1000msTest) {
-  srand(Clock::GetRealTimeClock()->TimeInMicroseconds());
   RunFairnessTest(GetParam(), 4, 0, 300, 3000, 1000);
 }
 
 TEST_P(BweFeedbackTest, TcpFairness50msTest) {
-  srand(Clock::GetRealTimeClock()->TimeInMicroseconds());
   RunFairnessTest(GetParam(), 1, 1, 300, 2000, 50);
 }
 
 TEST_P(BweFeedbackTest, TcpFairness500msTest) {
-  srand(Clock::GetRealTimeClock()->TimeInMicroseconds());
   RunFairnessTest(GetParam(), 1, 1, 300, 2000, 500);
 }
 
 TEST_P(BweFeedbackTest, TcpFairness1000msTest) {
-  srand(Clock::GetRealTimeClock()->TimeInMicroseconds());
   RunFairnessTest(GetParam(), 1, 1, 300, 2000, 1000);
 }
 }  // namespace bwe