Simplify some code using SelectionTemplate::ComputeRange()

I added a helper method, SelectionTemplate::ComputeRange() in this CL:
https://chromium-review.googlesource.com/c/chromium/src/+/806439

This CL migrates some callers over to using this new method.

Change-Id: I44557d6fb5b401d1e3ca066612b11ad57be27d82
Reviewed-on: https://chromium-review.googlesource.com/808753Reviewed-by: yosin (OOO Dec 11 to Jan 8) <yosin@chromium.org>
Commit-Queue: Ryan Landay <rlanday@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522009}

third_party/WebKit/Source/core/editing/SelectionAdjuster.cpp

@@ -288,9 +288,8 @@ class ShadowBoundaryAdjuster final {
   template <typename Strategy>
   static SelectionTemplate<Strategy> AdjustSelection(
       const SelectionTemplate<Strategy>& granularity_adjusted_selection) {
-    const EphemeralRangeTemplate<Strategy> expanded_range(
-        granularity_adjusted_selection.ComputeStartPosition(),
-        granularity_adjusted_selection.ComputeEndPosition());
+    const EphemeralRangeTemplate<Strategy> expanded_range =
+        granularity_adjusted_selection.ComputeRange();
 
     const EphemeralRangeTemplate<Strategy> shadow_adjusted_range =
         granularity_adjusted_selection.IsBaseFirst()
@@ -503,9 +502,8 @@ class EditingBoundaryAdjuster final {
   static SelectionTemplate<Strategy> AdjustSelection(
       const SelectionTemplate<Strategy>& shadow_adjusted_selection) {
     // TODO(editing-dev): Refactor w/o EphemeralRange.
-    const EphemeralRangeTemplate<Strategy> shadow_adjusted_range(
-        shadow_adjusted_selection.ComputeStartPosition(),
-        shadow_adjusted_selection.ComputeEndPosition());
+    const EphemeralRangeTemplate<Strategy> shadow_adjusted_range =
+        shadow_adjusted_selection.ComputeRange();
     const EphemeralRangeTemplate<Strategy> editing_adjusted_range =
         AdjustSelectionToAvoidCrossingEditingBoundaries(
             shadow_adjusted_range, shadow_adjusted_selection.Base());

third_party/WebKit/Source/core/editing/iterators/SimplifiedBackwardsTextIteratorTest.cpp

@@ -27,10 +27,8 @@ class SimplifiedBackwardsTextIteratorTest : public EditingTestBase {
     const SelectionInDOMTree selection = SetSelectionTextToBody(selection_text);
     StringBuilder builder;
     bool is_first = true;
-    for (SimplifiedBackwardsTextIterator iterator(
-             EphemeralRange(selection.ComputeStartPosition(),
-                            selection.ComputeEndPosition()),
-             behavior);
+    for (SimplifiedBackwardsTextIterator iterator(selection.ComputeRange(),
+                                                  behavior);
          !iterator.AtEnd(); iterator.Advance()) {
       BackwardsTextBuffer buffer;
       iterator.CopyTextTo(&buffer);