Add comments for two test expectations and move them to the right place.

webkit/tools/layout_tests/test_expectations.txt

 // This file consists of lines with specifications of what
 // to expect from layout test cases. The test cases can be directories
 // in which case the expectations apply to all test cases in that
 // directory and any subdirectory. The format of the file is along the
 // lines of:
 //
 // LayoutTests/fast/js/fixme.js = FAIL
 // LayoutTests/fast/js/flaky.js = FAIL PASS
 // LayoutTests/fast/js/crash.js = CRASH TIMEOUT FAIL PASS
 //
@@ skipping 1108 matching lines @@
 
 BUG10306 LINUX : LayoutTests/svg/carto.net/combobox.svg = FAIL
 
 // There are a ugly room between black strokes and white painting of characters.
 BUG10307 WIN : LayoutTests/svg/W3C-SVG-1.1/filters-example-01-b.svg = FAIL
 
 // Linux pixeltest failure: slightly different shade of composited
 // alpha in bottom group.
 BUG10310 LINUX : LayoutTests/svg/W3C-SVG-1.1/masking-opacity-01-b.svg = FAIL
 
+// Image mismatch: some green blocks are not displayed.
+// Started to fail WebKit upstream change r49757, and probably related to it.
+BUG25175 : LayoutTests/svg/W3C-SVG-1.1/masking-mask-01-b.svg = IMAGE
+
+// Image mismatch since WebKit r49757.
+// The difference is hard to tell, but our gradation is slightly different
+// (blue is too strong on the gradation).
+// Pixel dump was updated on upstream but our rendering did not change.
+BUG25175 MAC : LayoutTests/svg/custom/grayscale-gradient-mask.svg = IMAGE
+
 //
 // -----------------------------------------------------------------
 // End of SVG tests
 // -----------------------------------------------------------------
 
 // These fail the pixel tests in debug mode because they have
 // unpainted space (filled red in Debug but not in Release).
 // https://bugs.webkit.org/show_bug.cgi?id=8423
 BUG24204 WIN LINUX : LayoutTests/tables/mozilla_expected_failures/bugs/bug178855.xml = IMAGE+TEXT
 
@@ skipping 2016 matching lines @@
 BUG25202 LINUX WIN : LayoutTests/svg/W3C-SVG-1.1/masking-path-02-b.svg = FAIL
 BUG25208 LINUX WIN : LayoutTests/svg/W3C-SVG-1.1/masking-path-05-f.svg = FAIL
 BUG_JEREMY LINUX WIN : LayoutTests/svg/custom/svg-fonts-in-html.html = FAIL
 BUG_JEREMY WIN : LayoutTests/editing/deleting/deletionUI-single-instance.html = FAIL
 BUG25204 WIN : chrome/fast/forms/basic-selects.html = FAIL
 BUG_JEREMY MAC : LayoutTests/fast/frames/onlyCommentInIFrame.html = CRASH FAIL
 BUG_JEREMY WIN : LayoutTests/fast/css/shadow-multiple.html = FAIL
 
 // WebKit Roll 49684:49761
 BUG_YUTAK : LayoutTests/fast/events/drag-and-drop-dataTransfer-types-nocrash.html = FAIL
-BUG_YUTAK : LayoutTests/svg/W3C-SVG-1.1/masking-mask-01-b.svg = FAIL
-BUG_YUTAK MAC : LayoutTests/svg/custom/grayscale-gradient-mask.svg = FAIL
 BUG_YUTAK LINUX : LayoutTests/http/tests/security/mixedContent/insecure-plugin-in-iframe.html = FAIL
 
 // WebKit Roll 49761:49809
 BUG_JAPHET LINUX WIN : LayoutTests/fast/canvas/arc360.html = FAIL
 BUG_JAPHET LINUX : LayoutTests/fast/css/transition-color-unspecified.html = FAIL
 BUG_JAPHET : LayoutTests/media/media-load-event.html = FAIL
 BUG_JAPHET : LayoutTests/media/progress-event-at-least-one.html = FAIL
 
 // WebKit Roll 49809:49830
 BUG_YUTAK LINUX : LayoutTests/svg/custom/marker-default-width-height.svg = FAIL
 BUG_YUTAK MAC : LayoutTests/svg/W3C-SVG-1.1/filters-diffuse-01-f.svg = FAIL