Bug 1301718: FaviconView extends AppCompatImageView. r=liuche

This change is unrelated to this bug.

According to my IDE warning:

```
This custom view should extend android.support.v7.widget.AppCompatImageView
instead.

In order to support features such as tinting, the appcompat library will
automatically load special appcompat replacements for the builtin widgets.
However, this does not work for your custom views.

Instead of extending the android.widget classes directly, you should instead
extend one of the delegate classes in android.support.v7.widget.AppCompat.
```

Seems reasonable and I don't see any documentation telling me not to. :)

MozReview-Commit-ID: H60bYGVgTIT

--HG--
extra : rebase_source : 68d193dcee21a53d1378669065a359504374fa72

mobile/android/base/java/org/mozilla/gecko/widget/FaviconView.java

@@ -6,6 +6,7 @@
 package org.mozilla.gecko.widget;
 
 import android.graphics.Color;
+import android.support.v7.widget.AppCompatImageView;
 import org.mozilla.gecko.R;
 import org.mozilla.gecko.icons.IconCallback;
 import org.mozilla.gecko.icons.IconResponse;
@@ -31,7 +32,7 @@ import java.lang.ref.WeakReference;
  * Displays solid colour background around Favicon to fill space not occupied by the icon. Colour
  * selected is the dominant colour of the provided Favicon.
  */
-public class FaviconView extends ImageView {
+public class FaviconView extends AppCompatImageView {
 
     // Default x/y-radius of the oval used to round the corners of the background (dp)
     private static final int DEFAULT_CORNER_RADIUS_DP = 2;