Replaced NULL with nullptr in Android CDM.

[ Merge of http://go/wvgerrit/85503 ]

Replacing a few instances of C's NULL with C++'s nullptr in some of the
smaller sub-directories in the CDM.

Note that clang-format has performed additional changes to some of the
test files that have not yet been formatted.

Bug: 120602075
Test: Android unittest
Change-Id: I926135ed4b85e9d2d58a014b4a62098b0cb7a373

libwvdrmengine/cdm/test/timer_unittest.cpp

@@ -22,7 +22,7 @@ class TestTimerHandler : public TimerHandler {
 
 TEST(TimerTest, ParametersCheck) {
   Timer timer;
-  EXPECT_FALSE(timer.Start(NULL, 10));
+  EXPECT_FALSE(timer.Start(nullptr, 10));
 
   TestTimerHandler handler;
   EXPECT_FALSE(timer.Start(&handler, 0));