Add forEach() to CSSVariablesMap

LayoutTests/fast/css/variables/cssom-foreach-expected.txt

Index: LayoutTests/fast/css/variables/cssom-foreach-expected.txt
diff --git a/LayoutTests/fast/css/variables/cssom-foreach-expected.txt b/LayoutTests/fast/css/variables/cssom-foreach-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..a11d94ed6b0b414f66c5b9f9d76423009a07530c
--- /dev/null
+++ b/LayoutTests/fast/css/variables/cssom-foreach-expected.txt
@@ -0,0 +1,13 @@
+Test calling forEach with no parameters: TypeError: Not enough arguments
+Test calling forEach with non-function as first argument: TypeError: Type error
+Test calling forEach with thisArg specified: pass
+Test adding variable in forEach: pass
+Test deleting in forEach: pass
+Test clearing in forEach: pass
+Test adding then deleting in forEach: pass
+Test adding then clearing in forEach: pass
+Test deleting then adding in forEach: pass
+Test clearing then adding in forEach: pass
+Test updating visited variable in forEach: pass
+Test nested forEach calls with addition and deletion: pass
+