Expose base::Callback::IsCancelled as WTF::Function::isCancelled

Review-Url: https://codereview.chromium.org/2327793002
Cr-Commit-Position: refs/heads/master@{#419113}

third_party/WebKit/Source/wtf/Functional.h

@@ -203,6 +203,11 @@ public:
         return m_callback.Run(std::forward<Args>(args)...);
     }
 
+    bool isCancelled() const
+    {
+        return m_callback.IsCancelled();
+    }
+
     friend base::Callback<R(Args...)> convertToBaseCallback(std::unique_ptr<Function> function)
     {
         return std::move(function->m_callback);

third_party/WebKit/Source/wtf/FunctionalTest.cpp

@@ -589,9 +589,11 @@ TEST(FunctionalTest, WeakPtr)
     std::unique_ptr<WTF::Closure> bound = WTF::bind(&HasWeakPtrSupport::increment, obj.createWeakPtr(), WTF::unretained(&counter));
 
     (*bound)();
+    EXPECT_FALSE(bound->isCancelled());
     EXPECT_EQ(1, counter);
 
     obj.revokeAll();
+    EXPECT_TRUE(bound->isCancelled());
     (*bound)();
     EXPECT_EQ(1, counter);
 }