Rewrite SamplingCircularQueue

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 98e5d9c483bf077f4a40f05d8856fe88e115eb97..478395aafd7e0c0fa2e60cc069ad4a87fca78a76 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -282,6 +282,10 @@ const int kOneByteSize    = kCharSize;
 const int kUC16Size     = sizeof(uc16);      // NOLINT
 
 
+// Round up n to be a multiple of sz, where sz is a power of 2.
+#define ROUND_UP(n, sz) (((n) + ((sz) - 1)) & ~((sz) - 1))
+
+
 // The expression OFFSET_OF(type, field) computes the byte-offset
 // of the specified field relative to the containing type. This
 // corresponds to 'offsetof' (in stddef.h), except that it doesn't