enable -Wunused-private-field for linux and chromeos.

chrome/browser/chromeos/input_method/input_method_engine.cc

Index: chrome/browser/chromeos/input_method/input_method_engine.cc
diff --git a/chrome/browser/chromeos/input_method/input_method_engine.cc b/chrome/browser/chromeos/input_method/input_method_engine.cc
index 39a41754b3252dd210526d4329e7d629a87bc3fa..bf9821929e0d2c55af754f96f8ea1f437be51fd2 100644
--- a/chrome/browser/chromeos/input_method/input_method_engine.cc
+++ b/chrome/browser/chromeos/input_method/input_method_engine.cc
@@ -525,8 +525,7 @@ void InputMethodEngineImpl::OnCandidateClicked(unsigned int index,
 class InputMethodEngineStub : public InputMethodEngine {
  public:
   InputMethodEngineStub()
-      : observer_(NULL), active_(false), next_context_id_(1),
-        context_id_(-1) {}
+      : observer_(NULL), active_(false) {}
 
   ~InputMethodEngineStub() {
   }
@@ -627,12 +626,6 @@ class InputMethodEngineStub : public InputMethodEngine {
   // True when this IME is active, false if deactive.
   bool active_;
 
-  // Next id that will be assigned to a context.
-  int next_context_id_;
-
-  // ID that is used for the current input context.  False if there is no focus.
-  int context_id_;
-
   // User specified id of this IME.
   std::string engine_id_;
 };