Change the caret color according to the lightness of the background color.

LayoutTests/editing/caret/caret-color-expected.txt

Index: LayoutTests/editing/caret/caret-color-expected.txt
diff --git a/LayoutTests/editing/caret/caret-color-expected.txt b/LayoutTests/editing/caret/caret-color-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..87a4996271b2919985fde79d29a2e0d57b5006b7
--- /dev/null
+++ b/LayoutTests/editing/caret/caret-color-expected.txt
@@ -0,0 +1,20 @@
+EDITING DELEGATE: shouldBeginEditingInDOMRange:range from 0 of DIV > BODY > HTML > #document to 3 of DIV > BODY > HTML > #document
+EDITING DELEGATE: webViewDidBeginEditing:WebViewDidBeginEditingNotification
+EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
+EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
+EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
+layer at (0,0) size 800x600
+  RenderView at (0,0) size 800x600
+layer at (0,0) size 800x600
+  RenderBlock {HTML} at (0,0) size 800x600
+    RenderBody {BODY} at (8,8) size 784x584
+      RenderBlock {P} at (0,0) size 784x40
+        RenderText {#text} at (0,0) size 703x39
+          text run at (0,0) width 703: "This tests to make sure that the caret is visible in the black background by getting the caret color from the color of the"
+          text run at (0,20) width 591: "element(span) containing the text, not the parent element(div) that has the contentEditable attribute."
+      RenderBlock {DIV} at (0,56) size 784x56 [border: (2px solid #FF0000)]
+        RenderInline {SPAN} at (0,0) size 186x27 [color=#FFFFFF] [bgcolor=#000000]
+          RenderText {#text} at (14,14) size 186x27
+            text run at (14,14) width 186: "Where is my caret?"
+        RenderText {#text} at (0,0) size 0x0
+caret: position 17 of child 0 {#text} of child 1 {SPAN} of child 3 {DIV} of body