Chromoting Android: Fix getActionBar() NullPointerException

s/getActionBar/getSupportActionBar in Desktop.java which uses
ActionBarActivity from the support library.

BUG=423875

Review URL: https://codereview.chromium.org/655243004

Cr-Commit-Position: refs/heads/master@{#299827}

remoting/android/java/src/org/chromium/chromoting/Desktop.java

@@ -140,7 +140,7 @@ public class Desktop extends ActionBarActivity implements View.OnSystemUiVisibil
 
     public void showActionBar() {
         mOverlayButton.setVisibility(View.INVISIBLE);
-        getActionBar().show();
+        getSupportActionBar().show();
 
         View decorView = getWindow().getDecorView();
         decorView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_VISIBLE);
@@ -149,7 +149,7 @@ public class Desktop extends ActionBarActivity implements View.OnSystemUiVisibil
     @SuppressLint("InlinedApi")
     public void hideActionBar() {
         mOverlayButton.setVisibility(View.VISIBLE);
-        getActionBar().hide();
+        getSupportActionBar().hide();
 
         View decorView = getWindow().getDecorView();