update SkSmallAllocator to force internal allocations to be 16-byte aligned

tests/SmallAllocatorTest.cpp

Index: tests/SmallAllocatorTest.cpp
diff --git a/tests/SmallAllocatorTest.cpp b/tests/SmallAllocatorTest.cpp
index 774e0c9e8982906f09def08548e98b2145ce1cf8..7c9172decc1ce5a4c482ff4e5d85737ae2ee440d 100644
--- a/tests/SmallAllocatorTest.cpp
+++ b/tests/SmallAllocatorTest.cpp
@@ -81,3 +81,16 @@ DEF_TEST(SmallAllocator_pointer, reporter) {
     REPORTER_ASSERT(reporter, container != nullptr);
     REPORTER_ASSERT(reporter, container->getDummy() == &d);
 }
+
+#define check_alignment(reporter, ptr)  \
+    REPORTER_ASSERT(reporter, SkIsAlign16((intptr_t)ptr))
+
+DEF_TEST(SmallAllocator_alignment, reporter) {
+    const size_t totalBytes = 1 + 2 + 4 + 8;
+    SkSmallAllocator<4, totalBytes> alloc;
+
+    check_alignment(reporter, alloc.reserveT<uint8_t>());
+    check_alignment(reporter, alloc.reserveT<uint16_t>());
+    check_alignment(reporter, alloc.reserveT<uint32_t>());
+    check_alignment(reporter, alloc.reserveT<uint64_t>());
+}