Fix unable to opt-in to crash reports & usage statistics from web-app

Cause:
The crash opt-in setting is sometimes controlled by domain policy, which will
prevent the user from enabling it.  However, this is not communicated to the
user properly.

Fix:
- Shows a tooltip "This setting is controlled by your domain policy" if
  necessary.
- Hides the check box if the domain doesn't allow usage stats collection
  as an empty disabled check box offers no value to the user.

BUG=388864

Review URL: https://codereview.chromium.org/898163002

Cr-Commit-Position: refs/heads/master@{#315105}

remoting/resources/remoting_strings.grd

@@ -1050,6 +1050,9 @@ For information about privacy, please see the Google Privacy Policy (http://goo.
       <message desc="Label for the button to decline sharing the computer in 'It2Me' mode." name="IDS_SHARE_CONFIRM_DIALOG_DECLINE" >
         Cancel
       </message>
+      <message desc="Text shown in tooltip to inform the user that a setting is managed by domain policy." name="IDS_SETTING_MANAGED_BY_POLICY">
+        This setting is managed by your domain policy.
+      </message>
 
     </messages>
   </release>

remoting/webapp/crd/js/host_setup_dialog.js

@@ -190,9 +190,21 @@ remoting.HostSetupDialog.prototype.showForStartWithToken_ =
    *     by policy.
    */
   function onGetConsent(supported, allowed, set_by_policy) {
-    that.usageStats_.hidden = !supported;
+    // Hide the usage stats check box if it is not supported or the policy
+    // doesn't allow usage stats collection.
+    var checkBoxLabel = that.usageStats_.querySelector('.checkbox-label');
+    that.usageStats_.hidden = !supported || (set_by_policy && !allowed);
     that.usageStatsCheckbox_.checked = allowed;
+
     that.usageStatsCheckbox_.disabled = set_by_policy;
+    checkBoxLabel.classList.toggle('disabled', set_by_policy);
+
+    if (set_by_policy) {
+      that.usageStats_.title = l10n.getTranslationOrError(
+          /*i18n-content*/ 'SETTING_MANAGED_BY_POLICY');
+    } else {
+      that.usageStats_.title = '';
+    }
   }
 
   /** @param {remoting.Error} error */
@@ -200,7 +212,7 @@ remoting.HostSetupDialog.prototype.showForStartWithToken_ =
     console.error('Error getting consent status: ' + error);
   }
 
-  this.usageStats_.hidden = false;
+  this.usageStats_.hidden = true;
   this.usageStatsCheckbox_.checked = false;
 
   // Prevent user from ticking the box until the current consent status is