Add TODO in InputInjector to separate clipboard handling

BUG=438096

Review URL: https://codereview.chromium.org/804173002

Cr-Commit-Position: refs/heads/master@{#308472}

remoting/host/input_injector.h

@@ -16,6 +16,7 @@ class SingleThreadTaskRunner;
 
 namespace remoting {
 
+// TODO(sergeyu): Move ClipboardStub implementation to Clipboard.
 class InputInjector : public protocol::ClipboardStub,
                       public protocol::InputStub {
  public: