Added an Evaluate Contrast button.

Evaluate Contrast tests the contrast between text color and background for
Views that may contain text. Sufficient contrast is defined as having a
contrast ratio of 4.5:1 in general, except for: Large text, which can have a
contrast ratio of only 3:1, Inactive components or pure decorations, and
text that is part of a logo or brand name.

Change-Id: Ib8bdb545e8407ff27531b743b2424784d5db52e5
Added tests for EvaluateContrastModel.

Tests cases where contrast ratio passes all tests, fails all tests, and where
results are indeterminate.

Change-Id: Icc09422fba9a56574b8db93a13e26fe8a680da89
Merge "Added an Evaluate Contrast button." into idea133
Merge "Added tests for EvaluateContrastModel." into idea133
hv: Add Junit as a test dependency

Change-Id: I0f123824475cf5cff506a83d2d561668a7db62a5
Merge "hv: Add Junit as a test dependency" into idea133
Disable hv tests from running on gradle check

Change-Id: Ie5b3d8b0b80550e805d34af478a45e3649d4c5a3
Merge "Disable hv tests from running on gradle check" into idea133
Revert "Disable hv tests from running on gradle check"

This reverts commit 618643a88ac8c30202b720db2e84b98e240bf1f9.
Merge "Revert "Disable hv tests from running on gradle check"" into idea133