Un-flaking TestSrtpError by using a fake clock.

This test verifies that SRTP errors are only signaled if a specific
amount of time has passed, and was using ProcessMessages(time) to
wait for an amount of time. But ProcessMessages may sometimes wait
for longer than the requested time (especially on TSAN bot, etc.).

BUG=webrtc:4690
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/2184083004 .

Cr-Commit-Position: refs/heads/master@{#13597}

webrtc/pc/channel_unittest.cc

diff --git a/webrtc/pc/channel_unittest.cc b/webrtc/pc/channel_unittest.cc
index 492c7d5..b36dcd1 100644
--- a/webrtc/pc/channel_unittest.cc
+++ b/webrtc/pc/channel_unittest.cc
@@ -12,6 +12,7 @@
 
 #include "webrtc/base/array_view.h"
 #include "webrtc/base/buffer.h"
+#include "webrtc/base/fakeclock.h"
 #include "webrtc/base/gunit.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/media/base/fakemediaengine.h"
@@ -1752,6 +1753,15 @@
         0x00, 0x00,
         0x00, 0x00,
         0x00, 0x01};
+
+    // Using fake clock because this tests that SRTP errors are signaled at
+    // specific times based on set_signal_silent_time.
+    rtc::ScopedFakeClock fake_clock;
+    // Some code uses a time of 0 as a special value, so we must start with
+    // a non-zero time.
+    // TODO(deadbeef): Fix this.
+    fake_clock.AdvanceTime(rtc::TimeDelta::FromSeconds(1));
+
     CreateChannels(RTCP | SECURE, RTCP | SECURE);
     EXPECT_FALSE(channel1_->secure());
     EXPECT_FALSE(channel2_->secure());
@@ -1777,11 +1787,11 @@
                              rtc::PacketOptions());
     // Wait for a while to ensure no message comes in.
     WaitForThreads();
-    rtc::Thread::Current()->ProcessMessages(200);
+    fake_clock.AdvanceTime(rtc::TimeDelta::FromMilliseconds(200));
     EXPECT_EQ(cricket::SrtpFilter::ERROR_NONE, error_handler.error_);
     EXPECT_EQ(cricket::SrtpFilter::UNPROTECT, error_handler.mode_);
     // Wait for a little more - the error will be triggered again.
-    rtc::Thread::Current()->ProcessMessages(200);
+    fake_clock.AdvanceTime(rtc::TimeDelta::FromMilliseconds(200));
     media_channel2_->SendRtp(kBadPacket, sizeof(kBadPacket),
                              rtc::PacketOptions());
     WaitForThreads();
@@ -1801,6 +1811,8 @@
     });
     EXPECT_EQ(cricket::SrtpFilter::ERROR_FAIL, error_handler.error_);
     EXPECT_EQ(cricket::SrtpFilter::UNPROTECT, error_handler.mode_);
+    // Terminate channels before the fake clock is destroyed.
+    EXPECT_TRUE(SendTerminate());
   }
 
   void TestOnReadyToSend() {