Improve GetWeakPtr() to better protect against unsafe usage patterns.

base/memory/weak_ptr_unittest.cc

Index: base/memory/weak_ptr_unittest.cc
diff --git a/base/memory/weak_ptr_unittest.cc b/base/memory/weak_ptr_unittest.cc
index 1a4870eab184e39f80fa2dd3d2b7abb797d61ab3..3584333ef57096e549653c8b1171f8bf4e21b31d 100644
--- a/base/memory/weak_ptr_unittest.cc
+++ b/base/memory/weak_ptr_unittest.cc
@@ -416,34 +416,6 @@ TEST(WeakPtrTest, MoveOwnershipImplicitly) {
   background.DeleteArrow(arrow);
 }
 
-TEST(WeakPtrTest, MoveOwnershipOfUnreferencedObject) {
-  BackgroundThread background;
-  background.Start();
-
-  Arrow* arrow;
-  {
-    Target target;
-    // Background thread creates WeakPtr.
-    background.CreateArrowFromTarget(&arrow, &target);
-
-    // Bind to background thread.
-    EXPECT_EQ(&target, background.DeRef(arrow));
-
-    // Release the only WeakPtr.
-    arrow->target.reset();
-
-    // Now we should be able to create a new reference from this thread.
-    arrow->target = target.AsWeakPtr();
-
-    // Re-bind to main thread.
-    EXPECT_EQ(&target, arrow->target.get());
-
-    // And the main thread can now delete the target.
-  }
-
-  delete arrow;
-}
-
 TEST(WeakPtrTest, MoveOwnershipAfterInvalidate) {
   BackgroundThread background;
   background.Start();