Fix broken rebaseline code

Fix broken rebaseline code

BUG=skia:
NOTRY=true

Committed: https://skia.googlesource.com/skia/+/10dc56c46899952b761817323fba9ee690b5bbd3

[kelvinly, 2014-06-10 22:14:47]

Increased margins slightly, hopefully won't break from the square root now

[benchen, 2014-06-10 22:18:21]

lgtm with a naming suggestion.

https://codereview.chromium.org/327943003/diff/20001/bench/gen_bench_expectat...
File bench/gen_bench_expectations.py (right):

https://codereview.chromium.org/327943003/diff/20001/bench/gen_bench_expectat...
bench/gen_bench_expectations.py:51: avg_squared = sum([bench**2 for bench in
benches])/len(benches)
avg_squared is not a very good name. avg_sum_squared is probably better.

[kelvinly, 2014-06-10 22:20:03]

Also added another abs() just to be on the safe side

https://codereview.chromium.org/327943003/diff/20001/bench/gen_bench_expectat...
File bench/gen_bench_expectations.py (right):

https://codereview.chromium.org/327943003/diff/20001/bench/gen_bench_expectat...
bench/gen_bench_expectations.py:51: avg_squared = sum([bench**2 for bench in
benches])/len(benches)
On 2014/06/10 22:18:21, benchen wrote:
> avg_squared is not a very good name. avg_sum_squared is probably better.

Done.

[kelvinly, 2014-06-10 22:20:08]

The CQ bit was checked by kelvinly@google.com

[commit-bot: I haz the power, 2014-06-10 22:20:36]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/kelvinly@google.com/327943003/40001

[commit-bot: I haz the power, 2014-06-10 22:20:38]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-06-10 22:20:38]

Failed to apply patch for bench/gen_bench_expectations.py:
While running git apply --index -p1;
  error: patch failed: bench/gen_bench_expectations.py:46
  error: bench/gen_bench_expectations.py: patch does not apply

Patch:       bench/gen_bench_expectations.py
Index: bench/gen_bench_expectations.py
diff --git a/bench/gen_bench_expectations.py b/bench/gen_bench_expectations.py
index
5a9e1e495b86c4d97d6151fdeaeb205cdbab07c7..1634914718f2237e6eb1f9d9ef3700bb6a386e27
100644
--- a/bench/gen_bench_expectations.py
+++ b/bench/gen_bench_expectations.py
@@ -46,13 +46,14 @@ def compute_ranges(benches):
   Returns:
     a list of float [lower_bound, upper_bound].
   """
-  minimum = min(benches)
-  maximum = max(benches)
-  diff = maximum - minimum
   avg = sum(benches) / len(benches)
+  squared_avg = avg ** 2
+  avg_sum_squared = sum([bench**2 for bench in benches])/len(benches)
+  std_dev = (abs(avg_sum_squared - squared_avg) + 0.05*abs(avg)) ** 0.5
 
-  return [minimum - diff * RANGE_RATIO_LOWER - avg * ERR_RATIO - ERR_LB,
-          maximum + diff * RANGE_RATIO_UPPER + avg * ERR_RATIO + ERR_UB]
+  # If the results are normally distributed, 2 standard deviations
+  # captures something like ~95% of the possible range of results I think
+  return [avg - 2*std_dev, avg + 2*std_dev]
 
 
 def create_expectations_dict(revision_data_points, builder):

[kelvinly, 2014-06-10 22:24:12]

The CQ bit was checked by kelvinly@google.com

[commit-bot: I haz the power, 2014-06-10 22:24:37]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/kelvinly@google.com/327943003/60001

[commit-bot: I haz the power, 2014-06-10 22:24:44]

Change committed as 10dc56c46899952b761817323fba9ee690b5bbd3