DEPS roll for trace_viewer ff2031:8f04ee

This roll picks the fixes for the unit test failues which was causing
irritating "Aw Snap!" crash of unit test renderer process in the latest
ToT of chromium and trace-viewer repos.

BUG=None
R=nduca,dsinclair,qyearsley
TESTS=None

Review URL: https://codereview.chromium.org/1025953002

Cr-Commit-Position: refs/heads/master@{#321799}

DEPS

@@ -131,7 +131,7 @@ deps = {
    Var('chromium_git') + '/crashpad/crashpad.git' + '@' + '82bebb11de699550a36bf411737d01880e4a16a7',
 
   'src/third_party/trace-viewer':
-   Var('chromium_git') + '/external/trace-viewer.git' + '@' + '8f04ee4ca080fa800a950cc5bcb2f18c65a5a5c6',
+   Var('chromium_git') + '/external/trace-viewer.git' + '@' + 'ff20313e37892c3c7f20c88bb22ab6f6e65659ae',
 
   'src/third_party/WebKit':
    Var('chromium_git') + '/chromium/blink.git' + '@' +  Var('webkit_revision'),