Allow removing distillability observers.

Bug: 1017341
Change-Id: I719f13dd45a75783dc919a0f74be996445951be6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875481Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Aran Gilman <gilmanmh@google.com>
Cr-Commit-Position: refs/heads/master@{#713868}

chrome/browser/dom_distiller/distillable_page_utils_browsertest.cc

@@ -249,4 +249,14 @@ IN_PROC_BROWSER_TEST_F(DistillablePageUtilsBrowserTestAllArticles,
       Optional(AllOf(Not(IsDistillable()), IsLast(), Not(IsMobileFriendly()))));
 }
 
+IN_PROC_BROWSER_TEST_F(DistillablePageUtilsBrowserTestAllArticles,
+                       ObserverNotCalledAfterRemoval) {
+  RemoveObserver(web_contents_, &holder_);
+  EXPECT_CALL(holder_, OnResult(_)).Times(0);
+  NavigateAndWait(kSimpleArticlePath, kWaitNoExpectedCall);
+  EXPECT_THAT(
+      GetLatestResult(web_contents_),
+      Optional(AllOf(IsDistillable(), IsLast(), Not(IsMobileFriendly()))));
+}
+
 }  // namespace dom_distiller

components/dom_distiller/content/browser/distillability_driver.cc

@@ -63,12 +63,6 @@ void DistillabilityDriver::CreateDistillabilityService(
       std::move(receiver));
 }
 
-void DistillabilityDriver::AddObserver(DistillabilityObserver* observer) {
-  if (!observers_.HasObserver(observer)) {
-    observers_.AddObserver(observer);
-  }
-}
-
 void DistillabilityDriver::OnDistillability(
     const DistillabilityResult& result) {
   latest_result_ = result;

components/dom_distiller/content/browser/distillability_driver.h

@@ -28,7 +28,9 @@ class DistillabilityDriver
   void CreateDistillabilityService(
       mojo::PendingReceiver<mojom::DistillabilityService> receiver);
 
-  void AddObserver(DistillabilityObserver* observer);
+  base::ObserverList<DistillabilityObserver>* GetObserverList() {
+    return &observers_;
+  }
   base::Optional<DistillabilityResult> GetLatestResult() const {
     return latest_result_;
   }

components/dom_distiller/content/browser/distillable_page_utils.cc

@@ -59,13 +59,34 @@ std::ostream& operator<<(std::ostream& os, const DistillabilityResult& result) {
 
 void AddObserver(content::WebContents* web_contents,
                  DistillabilityObserver* observer) {
+  DCHECK(observer);
   CHECK(web_contents);
   DistillabilityDriver::CreateForWebContents(web_contents);
 
   DistillabilityDriver* driver =
       DistillabilityDriver::FromWebContents(web_contents);
   CHECK(driver);
-  driver->AddObserver(observer);
+  base::ObserverList<DistillabilityObserver>* observer_list =
+      driver->GetObserverList();
+  if (!observer_list->HasObserver(observer)) {
+    observer_list->AddObserver(observer);
+  }
+}
+
+void RemoveObserver(content::WebContents* web_contents,
+                    DistillabilityObserver* observer) {
+  DCHECK(observer);
+  CHECK(web_contents);
+  DistillabilityDriver::CreateForWebContents(web_contents);
+
+  DistillabilityDriver* driver =
+      DistillabilityDriver::FromWebContents(web_contents);
+  CHECK(driver);
+  base::ObserverList<DistillabilityObserver>* observer_list =
+      driver->GetObserverList();
+  if (observer_list->HasObserver(observer)) {
+    observer_list->RemoveObserver(observer);
+  }
 }
 
 base::Optional<DistillabilityResult> GetLatestResult(

components/dom_distiller/content/browser/distillable_page_utils.h

@@ -40,11 +40,14 @@ class DistillabilityObserver : public base::CheckedObserver {
   virtual void OnResult(const DistillabilityResult& result) = 0;
 };
 
-// Set the delegate to receive the result of whether the page is distillable.
+// Add/remove objects to the list of observers to notify when the distillability
+// service returns a result.
 //
-// |web_contents| must be non-null.
+// |web_contents| and |observer| must both be non-null.
 void AddObserver(content::WebContents* web_contents,
                  DistillabilityObserver* observer);
+void RemoveObserver(content::WebContents* web_contents,
+                    DistillabilityObserver* observer);
 
 base::Optional<DistillabilityResult> GetLatestResult(
     content::WebContents* web_contents);