logd: fix various clang-tidy issues

In order of severity:
1) Add a CHECK() that a pointer is not nullptr, where the analyzer
   believes this is possible.
2) Add `final` appropriately to functions called from constructors.
3) Add missing cloexec flags.
4) Add missing `noexcept` and other subtle performance warnings

Test: build with clang-tidy
Change-Id: Ifd9a1299a51027a47382926b2224748b5750d6cf
diff --git a/logd/SerializedLogChunk.h b/logd/SerializedLogChunk.h
index 75cb936..a8ac8cd 100644
--- a/logd/SerializedLogChunk.h
+++ b/logd/SerializedLogChunk.h
@@ -25,7 +25,7 @@
 
 class SerializedLogChunk {
   public:
-    SerializedLogChunk(size_t size) : contents_(size) {}
+    explicit SerializedLogChunk(size_t size) : contents_(size) {}
     ~SerializedLogChunk();
 
     void Compress();