Read feature param for Physical Web experiment

chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWeb.java

 // 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.
 
 package org.chromium.chrome.browser.physicalweb;
 
 import android.content.Context;
 import android.os.AsyncTask;
+import android.text.TextUtils;
 
 import org.chromium.base.CommandLine;
 import org.chromium.chrome.browser.ChromeApplication;
 import org.chromium.chrome.browser.ChromeSwitches;
 import org.chromium.chrome.browser.ChromeVersionInfo;
+import org.chromium.components.variations.VariationsAssociatedData;
 
 /**
  * This class provides the basic interface to the Physical Web feature.
  */
 public class PhysicalWeb {
+    private static final String FIELD_TRIAL_NAME = "PhysicalWeb";
+    private static final String ENABLED_PARAM = "enabled";
+    private static final String ENABLED_VALUE = "true";
+
     /**
      * Evaluate whether the environment is one in which the Physical Web should
      * be enabled.
      * @return true if the PhysicalWeb should be enabled
      */
     public static boolean featureIsEnabled() {
+        // TODO(cco3): Remove chrome://flag after Finch is experiment is more in place.

[Alexei Svitkine (slow), 2015/12/16 20:11:30]

"Finch" is an internal codename. Don't use it in code or in the CL description.

         boolean allowedChannel =
                 ChromeVersionInfo.isLocalBuild() || ChromeVersionInfo.isDevBuild();
         boolean switchEnabled =
                 CommandLine.getInstance().hasSwitch(ChromeSwitches.ENABLE_PHYSICAL_WEB);

[Alexei Svitkine (slow), 2015/12/16 20:11:30]

You should also have a disable switch, so that if the experiment is putting
users into the enable group, they can disable it for debugging. In
about_flags.cc, you can use ENABLE_DISABLE_VALUE_TYPE() macro.

-        return allowedChannel && switchEnabled;
+        // Check chrome://flag, command line flag, and finch, in that order
+        return (allowedChannel && switchEnabled) || getBooleanParam(ENABLED_PARAM, false);

[Alexei Svitkine (slow), 2015/12/16 20:11:30]

The current logic won't integrate well with go/variations-flags set up.
Specifically, you won't be able to tag users who are using the flag in a
separate group. Which might be OK for you - such users will not show up in
either group on the variations dashboard. If you want to see them in a separate
group, you need to query the field trial regardless of the state of the flags as
per the example in the go link.

     }
 
     /**
      * Start the Physical Web feature.
      * At the moment, this only enables URL discovery over BLE.
      * @param application An instance of {@link ChromeApplication}, used to get the
      * appropriate PhysicalWebBleClient implementation.
      */
     public static void startPhysicalWeb(ChromeApplication application) {
         PhysicalWebBleClient physicalWebBleClient = PhysicalWebBleClient.getInstance(application);
@@ skipping 23 matching lines @@
 
     private static void clearUrlsAsync(final Context context) {
         Runnable task = new Runnable() {
             @Override
             public void run() {
                 UrlManager.getInstance(context).clearUrls();
             }
         };
         AsyncTask.THREAD_POOL_EXECUTOR.execute(task);
     }
+
+    /**
+     * Gets a boolean Finch parameter, assuming the <paramName>="true" format.  Also checks for a
+     * command-line switch with the same name, for easy local testing.

[nyquist, 2015/12/17 02:02:23]

Couldn't you force the trial through a command line instead?

+     * @param paramName The name of the Finch parameter (or command-line switch) to get a value for.
+     * @param defaultValue The default value to return when there's no param or switch.
+     * @return Whether the Finch param is defined with a value "true", if there's a command-line
+     *         flag present with any value.
+     */
+    private static boolean getBooleanParam(String paramName, boolean defaultValue) {
+        if (CommandLine.getInstance().hasSwitch(paramName)) {
+            return true;
+        }
+        String paramValue =
+                VariationsAssociatedData.getVariationParamValue(FIELD_TRIAL_NAME, paramName);
+        if (TextUtils.isEmpty(paramValue)) {
+            return defaultValue;
+        }
+        return TextUtils.equals(ENABLED_VALUE, paramValue);
+    }
 }