Add two regression tests for bugs already fixed

Author: slavapestov

test/decl/protocol/req/rdar123261282.swift

@@ -0,0 +1,21 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
+// RUN: %target-typecheck-verify-swift -disable-experimental-associated-type-inference
+
+struct CustomCollection<T>: RandomAccessCollection {
+    struct CustomIndices: RandomAccessCollection {
+        var count: Int { fatalError() }
+
+        var startIndex: Int { fatalError() }
+        var endIndex: Int { fatalError() }
+
+        subscript(index: Int) -> Int { fatalError() }
+    }
+
+    var count: Int { fatalError() }
+    var indices: CustomIndices { fatalError() }
+    var startIndex: Int { fatalError() }
+    var endIndex: Int { fatalError() }
+    func index(before i: Int) -> Int { fatalError() }
+    func index(after i: Int) -> Int { fatalError() }
+    subscript(index: Int) -> T { fatalError() }
+}

test/decl/protocol/req/rdar123270042.swift

@@ -0,0 +1,28 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
+// RUN: not %target-typecheck-verify-swift -disable-experimental-associated-type-inference
+
+func f<T: Sequence>(_: T) -> T.Element {}
+
+let x: Int = f(CustomCollection<Int>())
+
+struct CustomCollection<Element>: RandomAccessCollection, MutableCollection {
+    typealias SubSequence = ArraySlice<Element>
+    typealias Index = Int
+    typealias Indices = Range<Int>
+
+    var startIndex: Int { fatalError() }
+    var endIndex: Int { fatalError() }
+    var first: Element? { fatalError() }
+    var last: Element? { fatalError() }
+
+    subscript(position: Index) -> Element {
+        get { fatalError() }
+        set { fatalError() }
+    }
+
+    subscript(bounds: Indices) -> SubSequence {
+        get { fatalError() }
+        set { fatalError() }
+    }
+}
+