Fixes operator bool in InterfaceRequest

BUG=none
TEST=none

Change-Id: Iaa66929033aeea93fcbb31c2793f0251b3b7db8b
Reviewed-on: https://chromium-review.googlesource.com/944253Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540376}

mojo/public/cpp/bindings/interface_request.h

@@ -54,7 +54,7 @@ class InterfaceRequest {
   // Indicates whether the request currently contains a valid message pipe.
   bool is_pending() const { return handle_.is_valid(); }
 
-  explicit operator bool() const { return handle_; }
+  explicit operator bool() const { return handle_.is_valid(); }
 
   // Removes the message pipe from the request and returns it.
   ScopedMessagePipeHandle PassMessagePipe() { return std::move(handle_); }