Disable flaky DomDistillerViewerSourceBrowserTest.PrefChange test on Linux.

chrome/browser/dom_distiller/dom_distiller_viewer_source_browsertest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string.h>
 
 #include <memory>
 #include <utility>
 
 #include "base/command_line.h"
@@ skipping 506 matching lines @@
   std::string result;
   EXPECT_TRUE(content::ExecuteScriptAndExtractString(
       contents, kGetLoadIndicatorClassName, &result));
   EXPECT_EQ("hidden", result);
   EXPECT_TRUE(content::ExecuteScriptAndExtractString(
       contents, kGetContent , &result));
   EXPECT_THAT(result, HasSubstr("Page 1 content"));
   EXPECT_THAT(result, HasSubstr("Page 2 content"));
 }
 
-IN_PROC_BROWSER_TEST_F(DomDistillerViewerSourceBrowserTest, PrefChange) {
+// Flaky on Ubuntu-12.04 bots: https://crbug.com/606037
+#if defined(OS_LINUX)
+#define MAYBE_PrefChange DISABLED_PrefChange
+#else
+#define MAYBE_PrefChange PrefChange
+#endif
+IN_PROC_BROWSER_TEST_F(DomDistillerViewerSourceBrowserTest,
+                       MAYBE_PrefChange) {
   PrefTest(false);
 }
 
 #if defined(OS_LINUX)
 // Flaky on Ubuntu-12.04 bots: https://crbug.com/604362
 #define MAYBE_PrefChangeError DISABLED_PrefChangeError
 #else
 #define MAYBE_PrefChangeError PrefChangeError
 #endif
 IN_PROC_BROWSER_TEST_F(DomDistillerViewerSourceBrowserTest,
@@ skipping 107 matching lines @@
   EXPECT_EQ("dark serif", result);
   EXPECT_EQ(kDarkToolbarThemeColor, contents->GetThemeColor());
 
   EXPECT_TRUE(content::ExecuteScriptAndExtractString(
       contents, kGetFontSize, &result));
   base::StringToDouble(result, &fontSize);
   ASSERT_FLOAT_EQ(kScale, fontSize/oldFontSize);
 }
 
 }  // namespace dom_distiller