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

tests/SmallAllocatorTest.cpp

 /*
  * Copyright 2014 Google, Inc
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkSmallAllocator.h"
 #include "SkTypes.h"
 #include "Test.h"
@@ skipping 63 matching lines @@
 
 // Test that using a createT with a constructor taking a pointer as a
 // parameter works as expected.
 DEF_TEST(SmallAllocator_pointer, reporter) {
     SkSmallAllocator<1, 8> alloc;
     Dummy d;
     DummyContainer* container = alloc.createT<DummyContainer>(&d);
     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>());
+}