hide SkImageDecoder::Chooser

BUG=skia:
R=scroggo@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/331433003
diff --git a/src/images/SkImageDecoder_libico.cpp b/src/images/SkImageDecoder_libico.cpp
index c6dd6f0..e6ae16f 100644
--- a/src/images/SkImageDecoder_libico.cpp
+++ b/src/images/SkImageDecoder_libico.cpp
@@ -94,6 +94,7 @@
     if (length < (size_t)(6 + count*16))
         return false;
 
+#ifdef SK_SUPPORT_LEGACY_IMAGEDECODER_CHOOSER
     int choice;
     Chooser* chooser = this->getChooser();
     //FIXME:if no chooser, consider providing the largest color image
@@ -138,6 +139,9 @@
     //you never know what the chooser is going to supply
     if (choice >= count || choice < 0)
         return false;
+#else
+    const int choice = 0;   // TODO: fold this value into the expressions below
+#endif
 
     //skip ahead to the correct header
     //commented out lines are not used, but if i switch to other read method, need to know how many to skip