[test] Improve LineContinuation test coverage

The ECMAScript ⊃ JSON proposal doesn’t affect LineContinuation
grammar. These tests verify that the behavior remains the same when
the --harmony-subsume-json feature flag is enabled.

Bug: v8:7418
Change-Id: Iec5cb1bc112f278481ba1202f0c2b8693917843a
Reviewed-on: https://chromium-review.googlesource.com/1067463Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53270}

test/mjsunit/harmony/linecontinuation.js

+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-subsume-json
+
+// https://tc39.github.io/ecma262/#sec-literals-string-literals
+//
+// LineContinuation ::
+//   \ LineTerminatorSequence
+//
+// LineTerminatorSequence ::
+//   <LF>
+//   <CR>[lookahead ≠ <LF>]
+//   <LS>
+//   <PS>
+//   <CR><LF>
+
+// LineTerminatorSequence :: <LF>
+assertEquals('', eval('"\\\n"'));
+assertEquals('', eval("'\\\n'"));
+assertEquals('', eval('`\\\n`'));
+
+// LineTerminatorSequence :: <CR>[lookahead ≠ <LF>]
+assertEquals('', eval('"\\\r"'));
+assertEquals('', eval("'\\\r'"));
+assertEquals('', eval('`\\\r`'));
+
+// LineTerminatorSequence :: <LS>
+assertEquals('', eval('"\\\u2028"'));
+assertEquals('', eval("'\\\u2028'"));
+assertEquals('', eval('`\\\u2028`'));
+
+// LineTerminatorSequence :: <PS>
+assertEquals('', eval('"\\\u2029"'));
+assertEquals('', eval("'\\\u2029'"));
+assertEquals('', eval('`\\\u2029`'));
+
+// LineTerminatorSequence :: <CR><LF>
+assertEquals('', eval('"\\\r\n"'));
+assertEquals('', eval("'\\\r\n'"));
+assertEquals('', eval('`\\\r\n`'));

test/mjsunit/linecontinuation.js

+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://tc39.github.io/ecma262/#sec-literals-string-literals
+//
+// LineContinuation ::
+//   \ LineTerminatorSequence
+//
+// LineTerminatorSequence ::
+//   <LF>
+//   <CR>[lookahead ≠ <LF>]
+//   <LS>
+//   <PS>
+//   <CR><LF>
+
+// LineTerminatorSequence :: <LF>
+assertEquals('', eval('"\\\n"'));
+assertEquals('', eval("'\\\n'"));
+assertEquals('', eval('`\\\n`'));
+
+// LineTerminatorSequence :: <CR>[lookahead ≠ <LF>]
+assertEquals('', eval('"\\\r"'));
+assertEquals('', eval("'\\\r'"));
+assertEquals('', eval('`\\\r`'));
+
+// LineTerminatorSequence :: <LS>
+assertEquals('', eval('"\\\u2028"'));
+assertEquals('', eval("'\\\u2028'"));
+assertEquals('', eval('`\\\u2028`'));
+
+// LineTerminatorSequence :: <PS>
+assertEquals('', eval('"\\\u2029"'));
+assertEquals('', eval("'\\\u2029'"));
+assertEquals('', eval('`\\\u2029`'));
+
+// LineTerminatorSequence :: <CR><LF>
+assertEquals('', eval('"\\\r\n"'));
+assertEquals('', eval("'\\\r\n'"));
+assertEquals('', eval('`\\\r\n`'));