Increase allowed percentage of pixels that differ in...

Increase allowed percentage of pixels that differ in ImageBackgroundFilter.BackgroundFilterRotated_GL test

The old value was 3.1% and on Windows a Skia change causes slightly more pixels to be different. It is increased to 4%.
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2145043002
Cr-Commit-Position: refs/heads/master@{#405265}

cc/trees/layer_tree_host_pixeltest_filters.cc

@@ -438,7 +438,7 @@ class ImageBackgroundFilter : public LayerTreeHostFiltersPixelTest {
 
     // Allow some fuzziness so that this doesn't fail when Skia makes minor
     // changes to blur or rectangle rendering.
-    float percentage_pixels_large_error = 3.1f;
+    float percentage_pixels_large_error = 4.f;
     float percentage_pixels_small_error = 0.0f;
     float average_error_allowed_in_bad_pixels = 2.f;
     int large_error_allowed = 2;