Add support for experiments

This change refactors the options logic and adds support for
experiments: a new type of options which are not shown in the options
page (their usage will be similar to Chrome flags).

Experiments can be set from the
chrome-extension://{extension_id}/options/experiments.html page.

This code refactoring simplifies the options definition. Each option now
has a default value, and a context: the place where the option is set
(options, experiments, internal, deprecated).

Change-Id: I358ae07c832acae6b4536788c4dbe12a0e4730bf
diff --git a/src/options/experiments.html b/src/options/experiments.html
new file mode 100644
index 0000000..a49e6c9
--- /dev/null
+++ b/src/options/experiments.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+  <head>
+    <meta charset="utf-8">
+    <title>Experiments</title>
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <link rel="stylesheet" href="options.css">
+    <link rel="stylesheet" href="chrome_style/chrome_style.css">
+  </head>
+  <body>
+    <main>
+      <h1 data-i18n="experiments_title"></h1>
+      <p data-i18n="experiments_description"></p>
+      <form>
+        <div class="actions"><button id="save" data-i18n="save"></button></div>
+      </form>
+      <div id="save-indicator"></div>
+    </main>
+    <script src="../common/common.js"></script>
+    <script src="experiments_bit.js"></script>
+    <script src="options_common.js"></script>
+  </body>