Bug 997101 - Remove the SetCSSViewport call in TabChild::Observe that needlessly sets a default value that results in a lot of expensive reflow. r=kats

dom/ipc/TabChild.cpp

@@ -879,11 +879,6 @@ TabChild::Observe(nsISupports *aSubject,
 
         mContentDocumentIsDisplayed = true;
 
-        // Reset CSS viewport and zoom to default on new page, then
-        // calculate them properly using the actual metadata from the
-        // page.
-        SetCSSViewport(kDefaultViewportSize);
-
         // In some cases before-first-paint gets called before
         // RecvUpdateDimensions is called and therefore before we have an
         // mInnerSize value set. In such cases defer initializing the viewport