IDL: Add forEach() method to iterable<>/maplike<>/setlike<> interfaces

LayoutTests/webmidi/requestmidiaccess.html

Index: LayoutTests/webmidi/requestmidiaccess.html
diff --git a/LayoutTests/webmidi/requestmidiaccess.html b/LayoutTests/webmidi/requestmidiaccess.html
index 065ec388f8b93919dbb8b68e3f5aafee6df91456..6ec8bd07b6711eb1387fc35dc1b0af5ae6fcf079 100644
--- a/LayoutTests/webmidi/requestmidiaccess.html
+++ b/LayoutTests/webmidi/requestmidiaccess.html
@@ -42,6 +42,15 @@ function checkInputMap(inputs) {
     shouldBeFalse("inputs.has('MockOutputID')");
     shouldBe("inputs.get('MockInputID')", "input");
     shouldBeUndefined("inputs.get('MockOutputID')");
+    debug("inputs.forEach(...)");
+    inputs.forEach(function (input, key, map) {
+        window.forEachInput = input;
+        shouldBe("forEachInput", "input");
+        window.forEachInputKey = key;
+        shouldBe("forEachInputKey", "inputKey");
+        window.forEachMap = map;
+        shouldBe("forEachMap", "inputs");
+    });
 }
 
 function checkOutputMap(outputs) {
@@ -75,6 +84,15 @@ function checkOutputMap(outputs) {
     shouldBeFalse("outputs.has('MockInputID')");
     shouldBe("outputs.get('MockOutputID')", "output");
     shouldBeUndefined("outputs.get('MockInputID')");
+    debug("outputs.forEach(...)");
+    outputs.forEach(function (output, key, map) {
+        window.forEachOutput = output;
+        shouldBe("forEachOutput", "output");
+        window.forEachOutputKey = key;
+        shouldBe("forEachOutputKey", "outputKey");
+        window.forEachMap = map;
+        shouldBe("forEachMap", "outputs");
+    });
 }
 
 function successCallback1(a) {