Add prototype for warning.

Fixes build.

Review URL: https://codereview.chromium.org/15536007

git-svn-id: http://skia.googlecode.com/svn/trunk@9227 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index a258087..122996a 100644
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -867,6 +867,8 @@
  *  x and y must be non-NULL.
  */
 bool get_upper_left_from_offset(SkBitmap::Config config, size_t offset, size_t rowBytes,
+                                   int32_t* x, int32_t* y);
+bool get_upper_left_from_offset(SkBitmap::Config config, size_t offset, size_t rowBytes,
                                    int32_t* x, int32_t* y) {
     SkASSERT(x != NULL && y != NULL);
     if (0 == offset) {