editing: Fix build with GCC after #575975

GCC currently fails to build selection_adjuster.cc after 7bd29404a ("[Blink]
Avoid crossing editing boundaries selection"):

    ../../third_party/blink/renderer/core/editing/selection_adjuster.cc:607:13: error: explicit specialization in non-namespace scope ‘class blink::EditingBoundaryAdjuster’
       template <>
                 ^
    ../../third_party/blink/renderer/core/editing/selection_adjuster.cc:611:37: error: template-id ‘IsEditingBoundary<blink::EditingInFlatTreeStrategy>’ in declaration of primary template
           bool is_previous_node_editable) {
                                         ^

which can be fixed by specializing
EditingBoundaryAdjuster::IsEditingBoundary() outside of
EditingBoundaryAdjuster's declaration.

Bug: 819294, 847192
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I624d693c4b629aefc5ada45313cdcd7242a00a2d
Reviewed-on: https://chromium-review.googlesource.com/1143393
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Raphael Kubo da Costa (CET) <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#576542}
1 file changed