Remove unsafe align4 call

Align by 4 safely before calling malloc.

BUG=chromium:763972

Change-Id: I9278ae0df516adf3eb96fc390ad7318a47cbefa4
Reviewed-on: https://skia-review.googlesource.com/49760
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>

src/core/SkMask.cpp

@@ -45,7 +45,14 @@ uint8_t* SkMask::AllocImage(size_t size) {
 #ifdef TRACK_SKMASK_LIFETIME
     SkDebugf("SkMask::AllocImage %d\n", gCounter++);
 #endif
-    return (uint8_t*)sk_malloc_throw(SkAlign4(size));
+    size_t aligned_size = std::numeric_limits<size_t>::max();
+
+    // Expand size to next multiple of four.
+    size_t adjustment = 3;
+    if (size + adjustment > size) {
+        aligned_size = (size + adjustment) & ~adjustment;
+    }
+    return static_cast<uint8_t*>(sk_malloc_throw(aligned_size));
 }
 
 /** We explicitly use this allocator for SkBimap pixels, so that we can