Improve setting height of editor

Side affect is if you have the developer console open
the editor will be much smaller.

But this is worth the trade off.

Screenshot: https://imgur.com/a/OIwISAp
Change-Id: I07d923ee5038db7e0b03dddb7ccd74b019c3bf64

gr-editor/codemirror-element.js

diff --git a/gr-editor/codemirror-element.js b/gr-editor/codemirror-element.js
index 94ee213..d75db0f 100644
--- a/gr-editor/codemirror-element.js
+++ b/gr-editor/codemirror-element.js
@@ -63,9 +63,18 @@
     // eslint-disable-next-line new-cap
     this._nativeMirror = window.CodeMirror(this.$.wrapper, this._params);
     setTimeout(() => {
+      const offsetTop =
+          this._nativeMirror.display.wrapper.getBoundingClientRect().top;
+      const clientHeight =
+          window.innerHeight || document.clientHeight || document.getElementByTagName('body').clientHeight;
+      // We are setting a fixed height, because for large files we want to
+      // benefit from CodeMirror's virtual scrolling.
+      // 80px is roughly the size of the bottom margins plus the footer height.
+      // This ensures the height of the textarea doesn't push out of screen.
+      const height = clientHeight - offsetTop - 80;
       this._nativeMirror.refresh();
       this._nativeMirror.focus();
-      this._nativeMirror.setSize(null, window.screen.height);
+      this._nativeMirror.setSize(null, height < 600 ? 600 : height);
       if (this.lineNum) {
         // We have to take away one from the line number,
         // ... because CodeMirror's line count is zero-based.