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Fix source frame border extension

This commit fixes an issue in source frame border extension. It
causes certain frame resolution such as 640x480 to have a portion
of the right/bottom extension filled by zeros, which misleads
motion search and degrades transform coding performance when large
block size is used.

This fix improves the speed 2 compression performance of a few
yt sequence, typically ranging from 1% - 2%, up to 5% at median
to low bit-rate.

Change-Id: Id6b09a5695d9e7651c6dfbc2c6a72288b08af7fb

--- a/vp9/encoder/vp9_extend.c

+++ b/vp9/encoder/vp9_extend.c

@@ -110,9 +110,9 @@

   // Motion estimation may use src block variance with the block size up

   // to 64x64, so the right and bottom need to be extended to 64 multiple

   // or up to 16, whichever is greater.

-  const int eb_y = MAX(src->y_width + 16, ALIGN_POWER_OF_TWO(src->y_width, 6))

+  const int er_y = MAX(src->y_width + 16, ALIGN_POWER_OF_TWO(src->y_width, 6))

       - src->y_crop_width;

-  const int er_y = MAX(src->y_height + 16, ALIGN_POWER_OF_TWO(src->y_height, 6))

+  const int eb_y = MAX(src->y_height + 16, ALIGN_POWER_OF_TWO(src->y_height, 6))

       - src->y_crop_height;

   const int uv_width_subsampling = (src->uv_width != src->y_width);

   const int uv_height_subsampling = (src->uv_height != src->y_height);