Bug 1501665 Part 3: Add a new function to determine if a document can use resolution zooming. r=botond

Differential Revision: https://phabricator.services.mozilla.com/D19238

--HG--
extra : source : 731d7ee06d86794fb9ec58b32f1495ad11205a1c

layout/base/nsLayoutUtils.cpp

@@ -667,6 +667,16 @@ bool nsLayoutUtils::AsyncPanZoomEnabled(nsIFrame* aFrame) {
   return widget->AsyncPanZoomEnabled();
 }
 
+bool nsLayoutUtils::AllowZoomingForDocument(
+    const mozilla::dom::Document* aDocument) {
+  // True if we allow zooming for all documents on this platform, or if we are
+  // in RDM and handling meta viewports, which force zoom under some
+  // circumstances.
+  return gfxPrefs::APZAllowZooming() ||
+         (aDocument && aDocument->InRDMPane() &&
+          nsLayoutUtils::ShouldHandleMetaViewport(aDocument));
+}
+
 float nsLayoutUtils::GetCurrentAPZResolutionScale(nsIPresShell* aShell) {
   return aShell ? aShell->GetCumulativeNonRootScaleResolution() : 1.0;
 }
@@ -9783,7 +9793,7 @@ void nsLayoutUtils::ComputeSystemFont(nsFont* aSystemFont,
 }
 
 /* static */
-bool nsLayoutUtils::ShouldHandleMetaViewport(Document* aDocument) {
+bool nsLayoutUtils::ShouldHandleMetaViewport(const Document* aDocument) {
   auto metaViewportOverride = nsIDocShell::META_VIEWPORT_OVERRIDE_NONE;
   if (aDocument) {
     if (nsIDocShell* docShell = aDocument->GetDocShell()) {

layout/base/nsLayoutUtils.h

@@ -2703,6 +2703,12 @@ class nsLayoutUtils {
    */
   static float GetCurrentAPZResolutionScale(nsIPresShell* aShell);
 
+  /**
+   * Returns true if aDocument should be allowed to use resolution
+   * zooming.
+   */
+  static bool AllowZoomingForDocument(const mozilla::dom::Document* aDocument);
+
   /**
    * Returns true if we need to disable async scrolling for this particular
    * element. Note that this does a partial disabling - the displayport still
@@ -2995,7 +3001,7 @@ class nsLayoutUtils {
    * Returns true if there are any preferences or overrides that indicate a
    * need to create a MobileViewportManager.
    */
-  static bool ShouldHandleMetaViewport(mozilla::dom::Document*);
+  static bool ShouldHandleMetaViewport(const mozilla::dom::Document*);
 
   /**
    * Resolve a CSS <length-percentage> value to a definite size.