fix(interpolate): changes the interpolate function to escape double quotes

Fix a bug in the interpolate function causing it not to handle expressions containing double quotes properly.

Closes #937

Author: vsavkin

lib/core/interpolate.dart

@@ -49,7 +49,7 @@ class Interpolate implements Function {
         if (index < startIdx) {
           // Empty strings could be stripped thanks to the stringify
           // formatter
-          expParts.add('"${template.substring(index, startIdx)}"');
+          expParts.add(_wrapInQuotes(template.substring(index, startIdx)));
         }
         expParts.add('(' + template.substring(startIdx + startLen, endIdx) +
         '|stringify)');
@@ -58,11 +58,16 @@ class Interpolate implements Function {
         hasInterpolation = true;
       } else {
         // we did not find any interpolation, so add the remainder
-        expParts.add('"${template.substring(index)}"');
+        expParts.add(_wrapInQuotes(template.substring(index)));
         break;
       }
     }
 
     return !mustHaveExpression || hasInterpolation ? expParts.join('+') : null;
   }
+
+  String _wrapInQuotes(String s){
+    final escaped = s.replaceAll(r'\', r'\\').replaceAll(r'"', r'\"');
+    return '"$escaped"';
+  }
 }

test/core/interpolate_spec.dart

@@ -33,5 +33,9 @@ main() {
       .toEqual('"X\nY"+(A\n+B|stringify)+"C\nD"');
     });
 
+    it('should escape double quotes', (Interpolate interpolate) {
+      expect(interpolate(r'"{{a}}')).toEqual(r'"\""+(a|stringify)');
+      expect(interpolate(r'\"{{a}}')).toEqual(r'"\\\""+(a|stringify)');
+    });
   });
 }