[RenderText] Added chrome os exclusion from doesntClip test.

The GetStringSize has had some unfound errors that are now being found by an improvement to the unit test.  There is another bug (465583) that is intended to look into these standing issues.  For the short term, this CL will remove Chrome OS from the failing unit test (which is no worst than the situation prior to the unit test being improved).

BUG=468903

Review URL: https://codereview.chromium.org/1003273004

Cr-Commit-Position: refs/heads/master@{#321590}

ui/gfx/render_text_unittest.cc

@@ -2726,10 +2726,10 @@ TEST_F(RenderTextTest, TextDoesntClip) {
       // as if it is ignoring the SetDisplayRect shift by kTestSize.  This
       // appears to be a preexisting issue that wasn't revealed by the prior
       // unit tests.
-#elif defined(OS_MACOSX)
-      // TODO(dschuyler): On Windows (non-XP) and Mac smoothing draws left of
-      // text.  This appears to be a preexisting issue that wasn't revealed by
-      // the prior unit tests.
+#elif defined(OS_MACOSX) || defined(OS_CHROMEOS)
+      // TODO(dschuyler): On Windows (non-XP), Chrome OS and Mac smoothing draws
+      // left of text.  This appears to be a preexisting issue that wasn't
+      // revealed by the prior unit tests.
       rect_buffer.EnsureSolidRect(SK_ColorWHITE, 0, kTestSize, kTestSize - 1,
                                   string_size.height());
 #else