Update Material Design History colors.

ui/webui/resources/html/md_shared_styles.html

Index: ui/webui/resources/html/md_shared_styles.html
diff --git a/ui/webui/resources/html/md_shared_styles.html b/ui/webui/resources/html/md_shared_styles.html
new file mode 100644
index 0000000000000000000000000000000000000000..0f2a1409b43a17989cf7d5b3b8edb4dae995c2a5
--- /dev/null
+++ b/ui/webui/resources/html/md_shared_styles.html
@@ -0,0 +1,9 @@
+<link rel="import" href="chrome://resources/html/polymer.html">
+
+<style is="custom-style">
+
+:root {
+  --md-toolbar-background-color: rgb(52, 73, 94);

[Dan Beam, 2016/03/31 18:30:13]

why not just put --md-background-color here as well? (instead of a class and
another html document)

[Dan Beam, 2016/03/31 18:32:52]

also, i'm wondering the functional difference between what you're doing and
<style include="...">.

https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/res...
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/res...

[calamity, 2016/04/01 02:46:29]

https://www.polymer-project.org/1.0/docs/devguide/styling.html#custom-style

custom-style seems to be for theming purposes like setting color mixins across
the whole main document. Shared styles look more appropriate for sharing classes
across custom elements.

[calamity, 2016/04/01 02:46:29]

Wellllllll. You can't use the property in a top-level html page because no
custom property polyfill magic happens there (which was why I asked about native
custom properties, if that would even solve this problem).

I think that's why things like paper-styles.html have an accompanying
paper-styles-classes.html for the main document. (Also iron-flex-layout
classes/iron-flex-layout)

+}
+
+</style>