Show diff percentage for resemble mode Change-Id: I52c269745490c08994dd45b2b068d015da174aad

diff --git a/gr-resemble-diff-mode/gr-resemble-diff-mode.html b/gr-resemble-diff-mode/gr-resemble-diff-mode.html
index 0404bb5..94a155c 100644
--- a/gr-resemble-diff-mode/gr-resemble-diff-mode.html
+++ b/gr-resemble-diff-mode/gr-resemble-diff-mode.html

@@ -44,6 +44,7 @@
       <h2>Loading...</h2>
       <img id="imageDiff">
     </div>
+    <div>[[_difference]]% changed</div>
     <label>
       <input
           id="ignoreColorsToggle"

diff --git a/gr-resemble-diff-mode/gr-resemble-diff-mode.js b/gr-resemble-diff-mode/gr-resemble-diff-mode.js
index 8e706f0..999e475 100644
--- a/gr-resemble-diff-mode/gr-resemble-diff-mode.js
+++ b/gr-resemble-diff-mode/gr-resemble-diff-mode.js

@@ -25,6 +25,10 @@
         observer: '_handleColorChange',
         value: '#00ffff',
       },
+      _difference: {
+        type: Number,
+        value: 0,
+      },
       _ignoreColors: {
         type: Boolean,
         value: false,
@@ -61,6 +65,10 @@
       this.$.imageDiff.src = src;
     },
 
+    _setDifferenceValue(percentage) {
+      this._difference = percentage;
+    },
+
     _getDataUrl(image) {
       return 'data:' + image['type'] + ';base64,' + image['body'];
     },
@@ -92,6 +100,7 @@
           this._createDiffProcess(base, rev, this._ignoreColors)
               .onComplete(data => {
                 this._setImageDiffSrc(data.getImageDataUrl());
+                this._setDifferenceValue(data.misMatchPercentage);
                 this.loading = false;
                 resolve();
               });

diff --git a/gr-resemble-diff-mode/gr-resemble-diff-mode_test.html b/gr-resemble-diff-mode/gr-resemble-diff-mode_test.html
index ba3e9ca..d24aed6 100644
--- a/gr-resemble-diff-mode/gr-resemble-diff-mode_test.html
+++ b/gr-resemble-diff-mode/gr-resemble-diff-mode_test.html

@@ -61,6 +61,12 @@
       assert.equal(img.getAttribute('src'), src);
     });
 
+    test('_setDifferenceValue', () => {
+      const expected = 0.15;
+      element._setDifferenceValue(expected);
+      assert.equal(element._difference, expected);
+    });
+
     test('_maybeIgnoreColors', () => {
       const dummyProcess = {
         ignoreColors: sandbox.stub(),