Add signMask getter to Float32x4

sdk/lib/typed_data/dart2js/typed_data_dart2js.dart

Index: sdk/lib/typed_data/dart2js/typed_data_dart2js.dart
diff --git a/sdk/lib/typed_data/dart2js/typed_data_dart2js.dart b/sdk/lib/typed_data/dart2js/typed_data_dart2js.dart
index 0c761ff5fada6cf08d77cb9545de22cb4d3bf27c..2b5280de35f0958e85dddf5545779c361ee6c5bf 100644
--- a/sdk/lib/typed_data/dart2js/typed_data_dart2js.dart
+++ b/sdk/lib/typed_data/dart2js/typed_data_dart2js.dart
@@ -931,6 +931,15 @@ class Float32x4 {
   /// Extracted w value.
   double get w => _storage[3];
 
+  /// Extract the sign bits from each lane return them in the first 4 bits.
+  int get signMask {
+    int mx = (_storage[0] & 0x80000000) >> 31;
+    int my = (_storage[1] & 0x80000000) >> 31;
+    int mz = (_storage[2] & 0x80000000) >> 31;
+    int mw = (_storage[3] & 0x80000000) >> 31;
+    return mx | my << 1 | mz << 2 | mw << 3;
+  }
+
   Float32x4 get xxxx => _shuffle(0x0);
   Float32x4 get xxxy => _shuffle(0x40);
   Float32x4 get xxxz => _shuffle(0x80);