Normalize line breaks in all string literals, not just template strings.

This allows string literal line continuations to be stripped when the continuation uses /\r\n?/ at the break (not just /\n/). Line continuations will be stripped in all language modes, including modes that support them (ES5+) since they have no semantic value.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=196883605

src/com/google/javascript/jscomp/parsing/IRFactory.java

@@ -2993,10 +2993,11 @@ String normalizeRegex(LiteralToken token) {
 
   String normalizeString(LiteralToken token, boolean templateLiteral) {
     String value = token.value;
-    if (templateLiteral) {
-      // <CR><LF> and <CR> are normalized as <LF> for raw string value
-      value = value.replaceAll("\r\n?", "\n");
-    }
+    // <CR><LF> and <CR> are normalized as <LF>. For raw template literal string values: this is the
+    // spec behaviour. For regular string literals: they can only be part of a line continuation,
+    // which we want to scrub.
+    value = value.replaceAll("\r\n?", "\n");
+
     int start = templateLiteral ? 0 : 1; // skip the leading quote
     int cur = value.indexOf('\\');
     if (cur == -1) {

test/com/google/javascript/jscomp/parsing/ParserTest.java

@@ -2205,26 +2205,50 @@ public void testYield3() {
     parseError("function * f() { yield , yield; }");
   }
 
-  public void testStringLineContinuation() {
+  public void testStringLineContinuationWarningsByMode() {
+    String unrecommendedWarning =
+        "String continuations are not recommended. See"
+            + " https://google.github.io/styleguide/jsguide.html#features-strings-no-line-continuations";
+
     expectFeatures(Feature.STRING_CONTINUATION);
-    mode = LanguageMode.ECMASCRIPT3;
     strictMode = SLOPPY;
-    Node n = parseWarning(
+
+    mode = LanguageMode.ECMASCRIPT3;
+    parseWarning(
         "'one\\\ntwo';",
         requiresLanguageModeMessage(LanguageMode.ECMASCRIPT5, Feature.STRING_CONTINUATION),
+        unrecommendedWarning);
+
+    mode = LanguageMode.ECMASCRIPT5;
+    parseWarning("'one\\\ntwo';", unrecommendedWarning);
+
+    mode = LanguageMode.ECMASCRIPT6;
+    parseWarning("'one\\\ntwo';", unrecommendedWarning);
+  }
+
+  public void testStringLineContinuationNormalization() {
+    String unrecommendedWarning =
         "String continuations are not recommended. See"
-                + " https://google.github.io/styleguide/jsguide.html#features-strings-no-line-continuations");
+            + " https://google.github.io/styleguide/jsguide.html#features-strings-no-line-continuations";
+
+    expectFeatures(Feature.STRING_CONTINUATION);
+    mode = LanguageMode.ECMASCRIPT6;
+    strictMode = SLOPPY;
+
+    Node n = parseWarning("'one\\\ntwo';", unrecommendedWarning);
     assertThat(n.getFirstFirstChild().getString()).isEqualTo("onetwo");
 
-    mode = LanguageMode.ECMASCRIPT5;
-    parseWarning("'one\\\ntwo';", "String continuations are not recommended. See"
-        + " https://google.github.io/styleguide/jsguide.html#features-strings-no-line-continuations");
+    n = parseWarning("'one\\\rtwo';", unrecommendedWarning);
     assertThat(n.getFirstFirstChild().getString()).isEqualTo("onetwo");
 
-    mode = LanguageMode.ECMASCRIPT6;
-    parseWarning("'one\\\ntwo';", "String continuations are not recommended. See"
-        + " https://google.github.io/styleguide/jsguide.html#features-strings-no-line-continuations");
+    n = parseWarning("'one\\\r\ntwo';", unrecommendedWarning);
     assertThat(n.getFirstFirstChild().getString()).isEqualTo("onetwo");
+
+    n = parseWarning("'one \\\ntwo';", unrecommendedWarning);
+    assertThat(n.getFirstFirstChild().getString()).isEqualTo("one two");
+
+    n = parseWarning("'one\\\n two';", unrecommendedWarning);
+    assertThat(n.getFirstFirstChild().getString()).isEqualTo("one two");
   }
 
   public void testStringLiteral() {