Navi: Clear NTP background when 'Default' is selected

This fixes a couple issues: 1) It allows us to keep the 'Next' button
always enabled so that users can quickly exit the flow, 2) it clears the
background when the user selects a custom background, hits 'Next',
hits the browser's back button, and tries to go back to 'Default'

Bug: 938235
Change-Id: I3ede7c9a99b4e0b293143188f0743c022aa07d42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504127Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637965}

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/ntp_background_proxy.js

@@ -15,6 +15,8 @@ cr.define('nux', function() {
 
   /** @interface */
   class NtpBackgroundProxy {
+    clearBackground() {}
+
     /** @return {!Promise<!Array<!nux.NtpBackgroundData>>} */
     getBackgrounds() {}
 
@@ -30,6 +32,11 @@ cr.define('nux', function() {
 
   /** @implements {nux.NtpBackgroundProxy} */
   class NtpBackgroundProxyImpl {
+    /** @override */
+    clearBackground() {
+      return cr.sendWithPromise('clearBackground');
+    }
+
     /** @override */
     getBackgrounds() {
       return cr.sendWithPromise('getBackgrounds');

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/nux_ntp_background.html

@@ -207,7 +207,6 @@
         </div>
         <step-indicator model="[[indicatorModel]]"></step-indicator>
         <paper-button class="action-button"
-            disabled$="[[!hasValidSelectedBackground_(selectedBackground_)]]"
             on-click="onNextClicked_">
           $i18n{next}
           <iron-icon icon="cr:chevron-right"></iron-icon>

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/nux_ntp_background.js

@@ -168,6 +168,8 @@ Polymer({
   onNextClicked_: function() {
     if (this.selectedBackground_ && this.selectedBackground_.id > -1) {
       this.ntpBackgroundProxy_.setBackground(this.selectedBackground_.id);
+    } else {
+      this.ntpBackgroundProxy_.clearBackground();
     }
     welcome.navigateToNextStep();
   },

chrome/browser/ui/webui/welcome/nux/ntp_background_handler.cc

@@ -34,6 +34,11 @@ NtpBackgroundHandler::NtpBackgroundHandler() {}
 NtpBackgroundHandler::~NtpBackgroundHandler() {}
 
 void NtpBackgroundHandler::RegisterMessages() {
+  web_ui()->RegisterMessageCallback(
+      "clearBackground",
+      base::BindRepeating(&NtpBackgroundHandler::HandleClearBackground,
+                          base::Unretained(this)));
+
   web_ui()->RegisterMessageCallback(
       "getBackgrounds",
       base::BindRepeating(&NtpBackgroundHandler::HandleGetBackgrounds,
@@ -45,6 +50,12 @@ void NtpBackgroundHandler::RegisterMessages() {
                           base::Unretained(this)));
 }
 
+void NtpBackgroundHandler::HandleClearBackground(const base::ListValue* args) {
+  InstantService* instant_service =
+      InstantServiceFactory::GetForProfile(Profile::FromWebUI(web_ui()));
+  instant_service->SetCustomBackgroundURL(GURL(""));
+}
+
 void NtpBackgroundHandler::HandleGetBackgrounds(const base::ListValue* args) {
   AllowJavascript();
   CHECK_EQ(1U, args->GetSize());

chrome/browser/ui/webui/welcome/nux/ntp_background_handler.h

@@ -18,6 +18,7 @@ class NtpBackgroundHandler : public content::WebUIMessageHandler {
   void RegisterMessages() override;
 
   // Callbacks for JS APIs.
+  void HandleClearBackground(const base::ListValue* args);
   void HandleGetBackgrounds(const base::ListValue* args);
   void HandleSetBackground(const base::ListValue* args);
 

chrome/test/data/webui/welcome/nux_ntp_background_test.js

@@ -91,14 +91,6 @@ cr.define('onboarding_ntp_background_test', function() {
       });
     });
 
-    test('test disabling and enabling of the next button', function() {
-      const nextButton = testElement.shadowRoot.querySelector('.action-button');
-      assertTrue(nextButton.disabled);
-      testElement.shadowRoot.querySelectorAll('.ntp-background-grid-button')[1]
-          .click();
-      assertFalse(nextButton.disabled);
-    });
-
     test('test activating a background', function() {
       const options = testElement.shadowRoot.querySelectorAll(
           '.ntp-background-grid-button');
@@ -122,5 +114,14 @@ cr.define('onboarding_ntp_background_test', function() {
         assertEquals(backgrounds[0].id, id);
       });
     });
+
+    test('test clearing the background when default is selected', function() {
+      // select the default option and hit 'Next'
+      const options = testElement.shadowRoot.querySelectorAll(
+          '.ntp-background-grid-button');
+      options[0].click();
+      testElement.$$('.action-button').click();
+      return testNtpBackgroundProxy.whenCalled('clearBackground');
+    });
   });
 });

chrome/test/data/webui/welcome/test_ntp_background_proxy.js

@@ -6,6 +6,7 @@
 class TestNtpBackgroundProxy extends TestBrowserProxy {
   constructor() {
     super([
+      'clearBackground',
       'getBackgrounds',
       'preloadImage',
       'setBackground',
@@ -15,6 +16,11 @@ class TestNtpBackgroundProxy extends TestBrowserProxy {
     this.backgroundsList_ = [];
   }
 
+  /** @override */
+  clearBackground() {
+    this.methodCalled('clearBackground');
+  }
+
   /** @override */
   getBackgrounds() {
     this.methodCalled('getBackgrounds');