Implement Android Credential Manager and Autofill providers (#109)

android/provider-client/src/main/assets/provider_form.html

@@ -0,0 +1,14 @@
+<!doctype html>
+<html lang="en"><meta name="viewport" content="width=device-width, initial-scale=1">
+<title>IronStorage browser fixture</title>
+<style>body{font:20px sans-serif;padding:24px}input,button{display:block;font:inherit;margin:16px 0;padding:12px;max-width:100%;box-sizing:border-box}</style>
+<h1>Browser credential fixture</h1>
+<p>This local page uses public synthetic credentials. It sends no network requests.</p>
+<form autocomplete="on" onsubmit="return false">
+<label for="username">Username</label>
+<input id="username" name="username" type="text" autocomplete="username">
+<label for="password">Password</label>
+<input id="password" name="password" type="password" autocomplete="current-password">
+<button type="button" onclick="document.getElementById('status').textContent=document.getElementById('username').value==='fixture-alice'&&document.getElementById('password').value==='public-provider-fixture-password'?'Chrome received the expected synthetic credential':'The fixture has not been filled'">Verify filled fixture</button>
+</form><p id="status">Waiting for an explicit fill.</p>
+</html>