SK_ONCE for SkMatrix::I()

src/core/SkMatrix.cpp

Index: src/core/SkMatrix.cpp
diff --git a/src/core/SkMatrix.cpp b/src/core/SkMatrix.cpp
index 3a5ab622197694edfa89358ee3187b1ccff07042..d802e1c5653142add278d7402a973d70ed959375 100644
--- a/src/core/SkMatrix.cpp
+++ b/src/core/SkMatrix.cpp
@@ -8,6 +8,7 @@
 #include "SkMatrix.h"
 #include "Sk64.h"
 #include "SkFloatBits.h"
+#include "SkOnce.h"
 #include "SkScalarCompare.h"
 #include "SkString.h"
 
@@ -1893,13 +1894,14 @@ SkScalar SkMatrix::getMaxStretch() const {
     return SkScalarSqrt(largerRoot);
 }
 
+DEF_SK_ONCE(reset_identity_matrix, SkMatrix* identity) {
+    identity->reset();
+}
+
 const SkMatrix& SkMatrix::I() {
+    // If you can use C++11 now, you might consider replacing this with a constexpr constructor.
     static SkMatrix gIdentity;
-    static bool gOnce;
-    if (!gOnce) {
-        gIdentity.reset();
-        gOnce = true;
-    }
+    SK_ONCE(reset_identity_matrix, &gIdentity);
     return gIdentity;
 }