Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc

Index: webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc
diff --git a/webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc b/webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc
index 6e1b9761d9ff82adbbcbace1033bbfaf0b131233..3f094be6d939666f0f202f1272cf735f08f6ca38 100644
--- a/webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc
+++ b/webrtc/modules/audio_device/linux/latebindingsymboltable_linux.cc
@@ -76,8 +76,8 @@ static bool LoadSymbol(DllHandle handle,
                "Error loading symbol %s : %d", symbol_name, err);
     return false;
   } else if (!*symbol) {
-    WEBRTC_TRACE(kTraceError, kTraceAudioDevice, -1,
-               "Symbol %s is NULL", symbol_name);
+    WEBRTC_TRACE(kTraceError, kTraceAudioDevice, -1, "Symbol %s is null",
+                 symbol_name);
     return false;
   }
   return true;
@@ -87,7 +87,7 @@ static bool LoadSymbol(DllHandle handle,
 }
 
 // This routine MUST assign SOME value for every symbol, even if that value is
-// NULL, or else some symbols may be left with uninitialized data that the
+// null, or else some symbols may be left with uninitialized data that the
 // caller may later interpret as a valid address.
 bool InternalLoadSymbols(DllHandle handle,
                          int num_symbols,