Add support to scroll to line

Bug: Issue 12364
Change-Id: I0e58a78eb93acfcb6e4bee639a66710a6341660f

gr-editor/codemirror-element.js

diff --git a/gr-editor/codemirror-element.js b/gr-editor/codemirror-element.js
index 65182d8..22e3f74 100644
--- a/gr-editor/codemirror-element.js
+++ b/gr-editor/codemirror-element.js
@@ -20,6 +20,10 @@
      * @event content-change
      */
 
+    properties: {
+      lineNum: Number,
+    },
+
     ready() {
       this.scopeSubtree(this.$.wrapper, true);
     },
@@ -50,6 +54,11 @@
       this.async(() => {
         this._nativeMirror.refresh();
         this._nativeMirror.focus();
+        if (this.lineNum) {
+          // We have to take away one from the line number,
+          // ... because CodeMirror's line count is zero-based.
+          this._nativeMirror.setCursor(this.lineNum - 1);
+        }
       }, 1);
       this._addEventListeners();
     },

gr-editor/gr-editor.html

diff --git a/gr-editor/gr-editor.html b/gr-editor/gr-editor.html
index 74d01a8..3fe859b 100644
--- a/gr-editor/gr-editor.html
+++ b/gr-editor/gr-editor.html
@@ -16,7 +16,7 @@
 
 <dom-module id="gr-editor">
   <template>
-    <codemirror-element id="codemirror"></codemirror-element>
+    <codemirror-element id="codemirror" line-num="[[lineNum]]"></codemirror-element>
   </template>
   <script src="gr-editor.js"></script>
 </dom-module>

gr-editor/gr-editor.js

diff --git a/gr-editor/gr-editor.js b/gr-editor/gr-editor.js
index ee2f455..add4a96 100644
--- a/gr-editor/gr-editor.js
+++ b/gr-editor/gr-editor.js
@@ -31,6 +31,7 @@
     properties: {
       fileContent: String,
       fileType: String,
+      lineNum: Number,
       mirror: Object,
       prefs: Object,
       plugin: Object,