Corrections to make line highlighting robust, added tests

Lines now save correctly with different inputs, making sure that different inputs like enter, delete, paste and where it's deleted stay consistent when saving.
Included in the create/update  snippet/note tests the structure from lines highlighting saved to the files.

browser/components/CodeEditor.js

@@ -511,12 +511,50 @@ export default class CodeEditor extends React.Component {
 
   handleChange (editor, changeObject) {
     spellcheck.handleChange(editor, changeObject)
+
+    this.updateHighlight(editor, changeObject)
+
     this.value = editor.getValue()
     if (this.props.onChange) {
       this.props.onChange(editor)
     }
   }
 
+  incrementLines (start, linesAdded, linesRemoved, editor) {
+    let highlightedLines = editor.options.linesHighlighted
+
+    const totalHighlightedLines = highlightedLines.length
+
+    let offset = linesAdded - linesRemoved
+
+    // Store new items to be added as we're changing the lines
+    let newLines = []
+
+    let i = totalHighlightedLines
+
+    while (i--) {
+      const lineNumber = highlightedLines[i]
+
+      // Interval that will need to be updated
+      // Between start and (start + offset) remove highlight
+      if (lineNumber >= start) {
+        highlightedLines.splice(highlightedLines.indexOf(lineNumber), 1)
+
+        // Lines that need to be relocated
+        if (lineNumber >= (start + linesRemoved)) {
+          newLines.push(lineNumber + offset)
+        }
+      }
+    }
+
+    // Adding relocated lines
+    highlightedLines.push(...newLines)
+
+    if (this.props.onChange) {
+      this.props.onChange(editor)
+    }
+  }
+
   handleHighlight (editor, changeObject) {
     const lines = editor.options.linesHighlighted
 
@@ -532,6 +570,37 @@ export default class CodeEditor extends React.Component {
     }
   }
 
+  updateHighlight (editor, changeObject) {
+    const linesAdded = changeObject.text.length - 1
+    const linesRemoved = changeObject.removed.length - 1
+
+    // If no lines added or removed return
+    if (linesAdded === 0 && linesRemoved === 0) {
+      return
+    }
+
+    let start = changeObject.from.line
+
+    switch (changeObject.origin) {
+      case '+insert", "undo':
+        start += 1
+        break
+
+      case 'paste':
+      case '+delete':
+      case '+input':
+        if (changeObject.to.ch !== 0 || changeObject.from.ch !== 0) {
+          start += 1
+        }
+        break
+
+      default:
+        return
+    }
+
+    this.incrementLines(start, linesAdded, linesRemoved, editor)
+  }
+
   moveCursorTo (row, col) {}
 
   scrollToLine (event, num) {