Fix undefined reference errors in input_method_engine.cc for Chrome OS build.

chrome/browser/chromeos/input_method/ibus_keymap.cc

Index: chrome/browser/chromeos/input_method/ibus_keymap.cc
diff --git a/chrome/browser/chromeos/input_method/ibus_keymap.cc b/chrome/browser/chromeos/input_method/ibus_keymap.cc
index 7c9400f44e044e73efe72aee1d94d82988a446b0..e0ed66fc8f5b9691ea5b06611af45fae4d1021c9 100644
--- a/chrome/browser/chromeos/input_method/ibus_keymap.cc
+++ b/chrome/browser/chromeos/input_method/ibus_keymap.cc
@@ -8,6 +8,9 @@
 #include <ibus.h>
 #endif
 
+namespace chromeos {
+namespace input_method {
+
 #if defined(HAVE_IBUS)
 std::string GetIBusKey(int keyval) {
   // TODO: Ensure all keys are supported.
@@ -86,3 +89,6 @@ std::string GetIBusKeyCode(int keyval, int keycode) {
   return "";
 }
 #endif // HAVE_IBUS
+
+}  // namespace input_method
+}  // namespace chromeos