[AIRFLOW-1465] Fix serialization error of chart data when X is Date

[mrkm4ntr]

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-1465

Description

• Here are some details about my PR, including screenshots of any UI changes:
  In Python 3, the example on https://airflow.incubator.apache.org/profiling.html#chart-screenshot fails with the error message like 1496268000000 is not JSON serializable or Object of type 'int64' is not JSON serializable.
  The numpy.int64 values can't be converted to native types in df[col].index.tolist(), but df[col].index.get_values() returns pandas.Series and pandas.Series.tolist() can convert them to native types.
  See below.

• https://github.com/pandas-dev/pandas/blob/master/pandas/core/indexes/base.py#L572
• https://github.com/pandas-dev/pandas/blob/master/pandas/core/series.py#L1124

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

There are no tests of rendering chart originally, and that's hard to test.

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[codecov-io]

Codecov Report

Merging #2550 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2550      +/-   ##
==========================================
- Coverage   70.88%   70.85%   -0.03%     
==========================================
  Files         150      150              
  Lines       11585    11585              
==========================================
- Hits         8212     8209       -3     
- Misses       3373     3376       +3

Impacted Files	Coverage Δ
airflow/www/views.py	69.99% <0%> (ø)	⬆️
airflow/jobs.py	77.67% <0%> (-0.28%)	⬇️

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[bolkedebruin]

Please add tests. Absence of tests is no reason to not add any. Thanks!

[mrkm4ntr]

I attempted to add a test, but it was blocked by #2598.

[ron819]

@mrkm4ntr are you still working on this PR?

[ron819]

Wasn't this fixed in Pandas?
pandas-dev/pandas@b2009e6

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.