Histograms created using the histogram macros are stored in per-site global storage, so any histogram recorded before StatisticsRecorder::Initialize() are unregistered until the process exits.  HistogramTester relies on StatisticsRecorder, so depending on whether HistogramTester is created before or after a particular histogram macro is used, it may or may not be able to find the corresponding histogram.

Pull StatisticsRecorder::Initialize() into the test-suite initialization, which should run before any code under test.

BUG=658070

Review-Url: https://codereview.chromium.org/2435933004
Cr-Commit-Position: refs/heads/master@{#427508}