Roll trace-viewer DEPS to a9802a1

This patch rolls trace-viewer to:
https://github.com/google/trace-viewer/commit/a9802a1384185f9c7ee250ce67d3d24d07b11141

Review URL: https://codereview.chromium.org/910773003

Cr-Commit-Position: refs/heads/master@{#315368}

DEPS

@@ -128,7 +128,7 @@ deps = {
    Var('chromium_git') + '/external/colorama.git' + '@' + '799604a1041e9b3bc5d2789ecbd7e8db2e18e6b8',
 
   'src/third_party/trace-viewer':
-   Var('chromium_git') + '/external/trace-viewer.git' + '@' + '3470cc939061a9238695747557adc41eb35ed267',
+   Var('chromium_git') + '/external/trace-viewer.git' + '@' + 'a9802a1384185f9c7ee250ce67d3d24d07b11141',
 
   'src/third_party/WebKit':
    Var('chromium_git') + '/chromium/blink.git' + '@' +  Var('webkit_revision'),