Bug 1233762 - Use the nsIImageDocument's built-in shrink-to-fit feature, rather than reimplementing it poorly in Fennec front-end code. r=esawin

--HG--
extra : commitid : KiWag7NVRQN

mobile/android/chrome/content/browser.js

@@ -4691,17 +4691,14 @@ Tab.prototype = {
           }
           this.contentDocumentIsDisplayed = true;
 
+          if (contentDocument instanceof Ci.nsIImageDocument) {
+            contentDocument.shrinkToFit();
+          }
+
           let zoom = this.restoredSessionZoom();
           if (zoom) {
             this.setResolution(zoom, true);
           }
-
-          if (!this.restoredSessionZoom() && contentDocument.mozSyntheticDocument) {
-            let fitZoom = Math.min(gScreenWidth / contentDocument.body.scrollWidth,
-                                   gScreenHeight / contentDocument.body.scrollHeight);
-            this.setResolution(fitZoom, false);
-            this.sendViewportUpdate();  // recompute displayport
-          }
         }
         break;
     }