Add cr-checkbox to Chrome

ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.css

Index: ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.css
diff --git a/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.css b/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.css
new file mode 100644
index 0000000000000000000000000000000000000000..94e9c52d3466464cec69be44fcc47bc1e007c0e0
--- /dev/null
+++ b/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.css
@@ -0,0 +1,15 @@
+/* Copyright 2015 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file. */
+
+:host {
+  display: inline-block;
+}
+
+paper-checkbox::shadow #ink[checked] {
+  color: rgb(0, 150, 136);

[Jeremy Klein, 2015/02/11 01:55:36]

Can we share the color defs somewhere?

[Oren Blasberg, 2015/02/11 20:12:42]

Not sure! Any ideas, Michael or Steven?

Note that this styling may change once I update the element to 0.5.4 in a
separate cl which I intend to land before this one.

[stevenjb, 2015/02/11 20:35:02]

I agree that it would be nice to have something like a cr_elements.css file that
all cr_elements share. I have no idea what the best way to implement that would
be though, my CSS fu is pretty weak.

[michaelpg, 2015/02/11 20:40:34]

Yes! I just discovered <core-style> last night. We should come up with a good
general-purpose solution using it and then use that for our styling and theming.
It has the added advantage of letting other Web UI that use cr-elements easily
define their own themes.

Here's a simple example:
http://pastebin.com/sP2iNMng

But we may want to take it a bit further, i.e., define our own <core-style
id="cr-themes"> where we specify a bunch of background and foreground colors.
Then we can just use those values in cr-checkbox, cr-toggle-button, etc. instead
of defining the colors on each individual control.

Since we'd still like to have CSS in .css files, maybe we also wrap <core-style>
in a <cr-style> element which is capable of importing .css files and applying
the templating.

Outside the scope of this CL, but take a look and let me know what you think.

+}
+
+paper-checkbox::shadow #checkbox.checked {
+  border-color: rgb(0, 150, 136);
+}