Add SIMD 128 alignment support to Heap.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 7fdcc26cea74de84912a03291a9ce9b4b1015b98..c73f395cb6808672ffc19863112facb8c32c4752 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -197,6 +197,8 @@ typedef int32_t uc32;
 const int kOneByteSize    = kCharSize;
 const int kUC16Size     = sizeof(uc16);      // NOLINT
 
+// 128 bit SIMD value size.
+const int kSimd128Size = 16;
 
 // 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))
@@ -309,6 +311,10 @@ const intptr_t kPointerAlignmentMask = kPointerAlignment - 1;
 const intptr_t kDoubleAlignment = 8;
 const intptr_t kDoubleAlignmentMask = kDoubleAlignment - 1;
 
+// Desired alignment for 128 bit SIMD values.
+const intptr_t kSimd128Alignment = 16;
+const intptr_t kSimd128AlignmentMask = kSimd128Alignment - 1;
+
 // Desired alignment for generated code is 32 bytes (to improve cache line
 // utilization).
 const int kCodeAlignmentBits = 5;
@@ -449,7 +455,12 @@ enum AllocationSpace {
 const int kSpaceTagSize = 3;
 const int kSpaceTagMask = (1 << kSpaceTagSize) - 1;
 
-enum AllocationAlignment { kWordAligned, kDoubleAligned, kDoubleUnaligned };
+enum AllocationAlignment {
+  kWordAligned,
+  kDoubleAligned,
+  kDoubleUnaligned,
+  kSimd128Unaligned
+};
 
 // A flag that indicates whether objects should be pretenured when
 // allocated (allocated directly into the old generation) or not