Marked a WebGL conformance test as FLAKY on Mac.

chrome/test/gpu/webgl_conformance_test_expectations.txt

Index: chrome/test/gpu/webgl_conformance_test_expectations.txt
diff --git a/chrome/test/gpu/webgl_conformance_test_expectations.txt b/chrome/test/gpu/webgl_conformance_test_expectations.txt
index d24a0fa95c0631addf743b816582a26c9d9b0bb2..c55d81529454af2aac1fed148a432b7b5ba04b61 100644
--- a/chrome/test/gpu/webgl_conformance_test_expectations.txt
+++ b/chrome/test/gpu/webgl_conformance_test_expectations.txt
@@ -12,6 +12,9 @@
 //
 //  91533 WIN : gl_min_uniforms = FAIL
 //    This will mark the test as FAILS_*.
+//
+//  91532 MAC : tex_image_and_sub_image_2d_with_video = PASS FAIL
+//    This will mark the test as FLAKY_*.
 
 // -----------------------------------------------------------------------------
 // SLOW TESTS
@@ -29,3 +32,9 @@
 91533 WIN : gl_min_uniforms = FAIL
 91533 WIN : oes_standard_derivatives = FAIL
 91533 WIN : texture_npot = FAIL
+
+// -----------------------------------------------------------------------------
+// FLAKY TESTS
+// -----------------------------------------------------------------------------
+
+92587 MAC : tex_image_and_sub_image_2d_with_video = PASS FAIL