Update test_expectations for some flaky tests

webkit/tools/layout_tests/test_expectations.txt

Index: webkit/tools/layout_tests/test_expectations.txt
===================================================================
--- webkit/tools/layout_tests/test_expectations.txt	(revision 30234)
+++ webkit/tools/layout_tests/test_expectations.txt	(working copy)
@@ -2553,7 +2553,7 @@
 
 // Was flaky. Became a consistent failure.
 BUG9798 WIN SLOW : LayoutTests/fast/replaced/border-radius-clip.html = FAIL
-BUG9798 MAC RELEASE : LayoutTests/http/tests/loading/preload-img-test.html = TIMEOUT PASS
+BUG9798 MAC WIN : LayoutTests/http/tests/loading/preload-img-test.html = TIMEOUT PASS
 BUG9798 LINUX DEBUG : LayoutTests/http/tests/local/style-access-before-stylesheet-loaded.html = FAIL PASS
 BUG9798 WIN DEBUG : LayoutTests/http/tests/local/style-access-before-stylesheet-loaded.html = FAIL PASS
 BUG9798 LINUX MAC : LayoutTests/http/tests/misc/BOM-override-script.html = TIMEOUT PASS
@@ -3084,8 +3084,6 @@
 BUG23956 WIN LINUX : LayoutTests/fast/dom/Range/getClientRects.html = FAIL
 BUG24126 : LayoutTests/fast/dom/HTMLInputElement/size-attribute.html = FAIL
 
-// WebKit update 48883:48904
-
 // WebKit update 48937:48947
 BUG23751 WIN LINUX DEBUG : LayoutTests/fast/inline/relative-positioned-overflow.html = CRASH
 
@@ -3255,3 +3253,6 @@
 BUG_JORLOW : LayoutTests/fast/css/getComputedStyle/computed-style.html = FAIL
 BUG_JORLOW RELEASE LINUX WIN : LayoutTests/svg/css/getComputedStyle-basic.xhtml = FAIL
 
+// Went flaky sometime after WebKit merge to 50073
+BUG_JAPHET LINUX : LayoutTests/fast/forms/textarea-placeholder-set-value.html = CRASH PASS
+