Replace NULL with nullptr in all C++ files.

webrtc/media/base/streamparams_unittest.cc

Index: webrtc/media/base/streamparams_unittest.cc
diff --git a/webrtc/media/base/streamparams_unittest.cc b/webrtc/media/base/streamparams_unittest.cc
index dc48a721acbc57407524b401c03f444e9d3bd9c6..d7978d8be5a2554b58b7f422868a5fa48e46eca0 100644
--- a/webrtc/media/base/streamparams_unittest.cc
+++ b/webrtc/media/base/streamparams_unittest.cc
@@ -92,7 +92,7 @@ TEST(StreamParams, HasSsrcGroup) {
 TEST(StreamParams, GetSsrcGroup) {
   cricket::StreamParams sp =
       CreateStreamParamsWithSsrcGroup("XYZ", kSsrcs2, arraysize(kSsrcs2));
-  EXPECT_EQ(NULL, sp.get_ssrc_group("xyz"));
+  EXPECT_EQ(nullptr, sp.get_ssrc_group("xyz"));
   EXPECT_EQ(&sp.ssrc_groups[0], sp.get_ssrc_group("XYZ"));
 }