add environment variable to scale to override default filtering

BUG=none
TEST=none
Review URL: https://webrtc-codereview.appspot.com/442001

git-svn-id: http://libyuv.googlecode.com/svn/trunk@209 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 208
+Version: 209
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,7 +11,7 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 208
+#define LIBYUV_VERSION 209
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_
 

source/scale.cc

@@ -12,6 +12,7 @@
 
 #include <assert.h>
 #include <string.h>
+#include <stdlib.h>  // For getenv()
 
 #include "libyuv/cpu_id.h"
 #include "libyuv/planar_functions.h"  // For CopyPlane
@@ -3636,6 +3637,13 @@ static void ScalePlane(const uint8* src, int src_stride,
                        uint8* dst, int dst_stride,
                        int dst_width, int dst_height,
                        FilterMode filtering, bool use_ref) {
+#ifdef CPU_X86
+  // environment variable overrides for testing.
+  char *filter_override = getenv("LIBYUV_FILTER");
+  if (filter_override) {
+    filtering = (FilterMode)atoi(filter_override);
+  }
+#endif
   // Use specialized scales to improve performance for common resolutions.
   // For example, all the 1/2 scalings will use ScalePlaneDown2()
   if (dst_width == src_width && dst_height == src_height) {