Replace NULL with nullptr in all C++ files.

webrtc/pc/externalhmac.cc

Index: webrtc/pc/externalhmac.cc
diff --git a/webrtc/pc/externalhmac.cc b/webrtc/pc/externalhmac.cc
index ec71833d752e57ba014edb4122b017e8b10ee6f2..bcb57c8e0fdf20140345c2c334326539a5a4ad23 100644
--- a/webrtc/pc/externalhmac.cc
+++ b/webrtc/pc/externalhmac.cc
@@ -37,14 +37,14 @@ static const uint8_t kExternalHmacFakeTag[10] = {
 };
 
 static const srtp_auth_test_case_t kExternalHmacTestCase0 = {
-  20,                                                    // Octets in key
-  const_cast<uint8_t*>(kExternalHmacTestCase0Key),   // Key
-  8,                                                     // Octets in data
-  const_cast<uint8_t*>(kExternalHmacTestCase0Data),  // Data
-  10,                                                    // Octets in tag
-  const_cast<uint8_t*>(kExternalHmacFakeTag),          // Tag
-  NULL                                                   // Pointer to next
-                                                         // testcase
+    20,                                                // Octets in key
+    const_cast<uint8_t*>(kExternalHmacTestCase0Key),   // Key
+    8,                                                 // Octets in data
+    const_cast<uint8_t*>(kExternalHmacTestCase0Data),  // Data
+    10,                                                // Octets in tag
+    const_cast<uint8_t*>(kExternalHmacFakeTag),        // Tag
+    nullptr                                            // Pointer to next
+                                                       // testcase
 };
 
 static const char kExternalHmacDescription[] =
@@ -80,7 +80,7 @@ srtp_err_status_t external_hmac_alloc(srtp_auth_t** a,
 
   // Allocate memory for auth and hmac_ctx_t structures.
   pointer = new uint8_t[(sizeof(ExternalHmacContext) + sizeof(srtp_auth_t))];
-  if (pointer == NULL)
+  if (pointer == nullptr)
     return srtp_err_status_alloc_fail;
 
   // Set pointers