[tools] Handle benchmark runs reporting more than one result.

The Wasm suite reports both compile time and code size, however,
perf-to-html.py elides one of the results (compile time, in this case).

This affects the effectiveness of results reported by perf try bot runs.

This CL addresses that.

BUG=

Review-Url: https://codereview.chromium.org/1941573002
Cr-Commit-Position: refs/heads/master@{#35935}

tools/perf-to-html.py

@@ -115,8 +115,8 @@ class Benchmark:
     self.name_ = name
     self.tests_ = {}
     for test in data:
-      # strip off "<name>/" prefix
-      test_name = test.split("/")[1]
+      # strip off "<name>/" prefix, allowing for subsequent "/"s
+      test_name = test.split("/", 1)[1]
       self.appendResult(test_name, data[test])
 
   # tests is a dictionary of Results