[Foundation overlay] Enable custom AnyHashable representation for NSMeasurement

Enables the overlay behavior blocked by rdar://problem/27539951.

(cherry picked from commit fa4331b)

Author: DougGregor

stdlib/public/SDK/Foundation/Measurement.swift

@@ -227,10 +227,6 @@ extension Measurement : _ObjectiveCBridgeable {
     }
 }
 
-/*
-FIXME(id-as-any): can't write this code because of:
-<rdar://problem/27539951> "unhandled generic bridged type" when bridging NSMeasurement
-
 @available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
 extension NSMeasurement : _HasCustomAnyHashableRepresentation {
     // Must be @nonobjc to avoid infinite recursion during bridging.
@@ -239,7 +235,6 @@ extension NSMeasurement : _HasCustomAnyHashableRepresentation {
         return AnyHashable(self as Measurement)
     }
 }
-*/
 
 // This workaround is required for the time being, because Swift doesn't support covariance for Measurement (26607639)
 @available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)

test/1_stdlib/TestMeasurement.swift

@@ -147,6 +147,36 @@ class TestMeasurement : TestMeasurementSuper {
         expectTrue(fiveKM < sevenThousandM)
         expectTrue(fiveKM <= fiveThousandM)
     }
+
+    func test_AnyHashableContainingMeasurement() {
+        let values: [Measurement<UnitLength>] = [
+          Measurement(value: 100, unit: UnitLength.meters),
+          Measurement(value: 100, unit: UnitLength.kilometers),
+          Measurement(value: 100, unit: UnitLength.kilometers),
+        ]
+        let anyHashables = values.map(AnyHashable.init)
+        expectEqual(Measurement<UnitLength>.self, type(of: anyHashables[0].base))
+        expectEqual(Measurement<UnitLength>.self, type(of: anyHashables[1].base))
+        expectEqual(Measurement<UnitLength>.self, type(of: anyHashables[2].base))
+        expectNotEqual(anyHashables[0], anyHashables[1])
+        expectEqual(anyHashables[1], anyHashables[2])
+    }
+
+    func test_AnyHashableCreatedFromNSMeasurement() {
+        if #available(iOS 8.0, *) {
+            let values: [NSMeasurement] = [
+                NSMeasurement(doubleValue: 100, unit: UnitLength.meters),
+                NSMeasurement(doubleValue: 100, unit: UnitLength.kilometers),
+                NSMeasurement(doubleValue: 100, unit: UnitLength.kilometers),
+            ]
+            let anyHashables = values.map(AnyHashable.init)
+            expectEqual(Measurement.self, type(of: anyHashables[0].base))
+            expectEqual(Measurement.self, type(of: anyHashables[1].base))
+            expectEqual(Measurement.self, type(of: anyHashables[2].base))
+            expectNotEqual(anyHashables[0], anyHashables[1])
+            expectEqual(anyHashables[1], anyHashables[2])
+        }
+    }
 }
 
 #if !FOUNDATION_XCTEST
@@ -159,6 +189,8 @@ if #available(OSX 10.12, iOS 10.0, tvOS 10.0, watchOS 3.0, *) {
     MeasurementTests.test("testMeasurementFormatter") { TestMeasurement().testMeasurementFormatter() }
     MeasurementTests.test("testEquality") { TestMeasurement().testEquality() }
     MeasurementTests.test("testComparison") { TestMeasurement().testComparison() }
+    MeasurementTests.test("test_AnyHashableContainingMeasurement") { TestMeasurement().test_AnyHashableContainingMeasurement() }
+  MeasurementTests.test("test_AnyHashableCreatedFromNSMeasurement") { TestMeasurement().test_AnyHashableCreatedFromNSMeasurement() }
     runAllTests()
 }
 #endif