Bug 1197824 - Stop propagating the default zoom around unnecessarily. r=snorp

The default zoom value is only used on the Java side to clamp the min/max zoom
values in the case where zooming is disabled. We can do this much earlier in
the flow, when we are computing the metadata, and reduce the amount of
redundant information being passed around.

mobile/android/base/gfx/JavaPanZoomController.java

@@ -1045,14 +1045,11 @@ class JavaPanZoomController
 
         ZoomConstraints constraints = mTarget.getZoomConstraints();
 
-        if (constraints.getMinZoom() > 0)
+        if (constraints.getMinZoom() > 0 || !constraints.getAllowZoom()) {
             minZoomFactor = constraints.getMinZoom();
-        if (constraints.getMaxZoom() > 0)
+        }
+        if (constraints.getMaxZoom() > 0 || !constraints.getAllowZoom()) {
             maxZoomFactor = constraints.getMaxZoom();
-
-        if (!constraints.getAllowZoom()) {
-            // If allowZoom is false, clamp to the default zoom level.
-            maxZoomFactor = minZoomFactor = constraints.getDefaultZoom();
         }
 
         // Ensure minZoomFactor keeps the page at least as big as the viewport.