Update sync::WeakHandle to use WeakPtr<T>::get()

sync/internal_api/public/util/weak_handle.h

Index: sync/internal_api/public/util/weak_handle.h
diff --git a/sync/internal_api/public/util/weak_handle.h b/sync/internal_api/public/util/weak_handle.h
index 57a44bd03b02f35242ca3f1eeac3daf866872cc3..c299be719c9f63ee5680b6525b1b57f2abbb1eb0 100644
--- a/sync/internal_api/public/util/weak_handle.h
+++ b/sync/internal_api/public/util/weak_handle.h
@@ -211,7 +211,7 @@ class WeakHandleCore
     if (!Get()) {
       return;
     }
-    (Get()->*fn)();
+    (Get().get()->*fn)();
   }
 
   template <typename U, typename A1>
@@ -221,7 +221,7 @@ class WeakHandleCore
     if (!Get()) {
       return;
     }
-    (Get()->*fn)(a1);
+    (Get().get()->*fn)(a1);
   }
 
   template <typename U, typename A1, typename A2>
@@ -232,7 +232,7 @@ class WeakHandleCore
     if (!Get()) {
       return;
     }
-    (Get()->*fn)(a1, a2);
+    (Get().get()->*fn)(a1, a2);
   }
 
   template <typename U, typename A1, typename A2, typename A3>
@@ -244,7 +244,7 @@ class WeakHandleCore
     if (!Get()) {
       return;
     }
-    (Get()->*fn)(a1, a2, a3);
+    (Get().get()->*fn)(a1, a2, a3);
   }
 
   template <typename U, typename A1, typename A2, typename A3, typename A4>
@@ -257,7 +257,7 @@ class WeakHandleCore
     if (!Get()) {
       return;
     }
-    (Get()->*fn)(a1, a2, a3, a4);
+    (Get().get()->*fn)(a1, a2, a3, a4);
   }
 
   // Must be dereferenced only on the owner thread.  May be destroyed