Modernize SkMutex and SkSemaphore.

include/private/SkMutex.h

Index: include/private/SkMutex.h
diff --git a/include/private/SkMutex.h b/include/private/SkMutex.h
index 8c78e1205c8796261be4b19468338a00af8afdc5..3b0e1c47ca16e34cbeeb6e2b7b3b12d006815670 100644
--- a/include/private/SkMutex.h
+++ b/include/private/SkMutex.h
@@ -8,33 +8,16 @@
 #ifndef SkMutex_DEFINED
 #define SkMutex_DEFINED
 
-// This file is not part of the public Skia API.
 #include "../private/SkSemaphore.h"
+#include "../private/SkThreadID.h"
 #include "SkTypes.h"
 
-#ifdef SK_DEBUG
-    #include "../private/SkThreadID.h"
-#endif
-
-#define SK_MUTEX_SEMAPHORE_INIT {1, {0}}
-
-#ifdef SK_DEBUG
-    #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0}
-#else
-    #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT}
-#endif
-
-// Using POD-style initialization prevents the generation of a static initializer.
-//
-// Without magic statics there are no thread safety guarantees on initialization
-// of local statics (even POD). As a result, it is illegal to use
-// SK_DECLARE_STATIC_MUTEX in a function.
-//
-// Because SkBaseMutex is not a primitive, a static SkBaseMutex cannot be
-// initialized in a class with this macro.
-#define SK_DECLARE_STATIC_MUTEX(name) namespace {} static SkBaseMutex name = SK_BASE_MUTEX_INIT;
-
-struct SkBaseMutex {
+#define SK_DECLARE_STATIC_MUTEX(name) static SkBaseMutex name;
+
+class SkBaseMutex {
+public:
+    constexpr SkBaseMutex() = default;
+
     void acquire() {
         fSemaphore.wait();
         SkDEBUGCODE(fOwner = SkGetThreadID();)
@@ -50,20 +33,15 @@ struct SkBaseMutex {
         SkASSERT(fOwner == SkGetThreadID());
     }
 
-    SkBaseSemaphore fSemaphore;
-    SkDEBUGCODE(SkThreadID fOwner;)
+protected:
+    SkBaseSemaphore fSemaphore{1};
+    SkDEBUGCODE(SkThreadID fOwner{kIllegalThreadID};)
 };
 
-// This needs to use subclassing instead of encapsulation to make SkAutoMutexAcquire to work.
 class SkMutex : public SkBaseMutex {
 public:
-    SkMutex () {
-        fSemaphore = SK_MUTEX_SEMAPHORE_INIT;
-        SkDEBUGCODE(fOwner = kIllegalThreadID);
-    }
-    ~SkMutex () { fSemaphore.deleteSemaphore(); }
-    SkMutex(const SkMutex&) = delete;
-    SkMutex& operator=(const SkMutex&) = delete;
+    using SkBaseMutex::SkBaseMutex;
+    ~SkMutex() { fSemaphore.cleanup(); }
 };
 
 template <typename Lock>