Metric for Chrome custom logic vs isLowRamDevice.

Detect how frequently the two definitions are identical. This will be
used to decide if we should switch to system-based implementation.

BUG=711079

Change-Id: Ibbb12df3cbf1523fd0e2fe5bb63a9ac3d91ea7cd
Reviewed-on: https://chromium-review.googlesource.com/738863
Commit-Queue: Maria Khomenko <mariakhomenko@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512021}

• base/android/java/src/org/chromium/base/SysUtils.java[diff]
• base/android/java/src/org/chromium/base/metrics/RecordHistogram.java[diff]
• tools/metrics/histograms/histograms.xml[diff]