Move paragraph granularity related tests to VisibleUnitsParagraphTest.cpp

This patch moves paragraph granularity related tests from "VisibleUnitsTest.cpp"
to "VisibleUnitsParagraphTest.cpp" for ease of maintenance.

Change-Id: I5bd49913a6407e2bcc74bda0a96aff3c7d066386
Reviewed-on: https://chromium-review.googlesource.com/970381Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544994}

third_party/WebKit/Source/core/editing/BUILD.gn

@@ -346,6 +346,7 @@ jumbo_source_set("unit_tests") {
     "VisiblePositionTest.cpp",
     "VisibleSelectionTest.cpp",
     "VisibleUnitsLineTest.cpp",
+    "VisibleUnitsParagraphTest.cpp",
     "VisibleUnitsSentenceTest.cpp",
     "VisibleUnitsTest.cpp",
     "VisibleUnitsWordTest.cpp",