Bug 1915051 - Early-exit UpdateResolutionForViewportSizeChange in fullscreen mode. r=hiro

Depends on D221391

Differential Revision: https://phabricator.services.mozilla.com/D221392

Author: theres-waldo

gfx/layers/apz/test/gtest/mvm/TestMobileViewportManager.cpp

@@ -81,6 +81,7 @@ class MockMVMContext : public MVMContext {
   bool AllowZoomingForDocument() const { return true; }
   bool IsInReaderMode() const { return false; }
   bool IsDocumentLoading() const { return false; }
+  bool IsDocumentFullscreen() const { return false; }
 
   void SetResolutionAndScaleTo(float aResolution,
                                ResolutionChangeOrigin aOrigin) {

layout/base/GeckoMVMContext.cpp

@@ -143,6 +143,11 @@ bool GeckoMVMContext::IsDocumentLoading() const {
   return mDocument->GetReadyStateEnum() == dom::Document::READYSTATE_LOADING;
 }
 
+bool GeckoMVMContext::IsDocumentFullscreen() const {
+  MOZ_ASSERT(mDocument);
+  return mDocument->Fullscreen();
+}
+
 void GeckoMVMContext::SetResolutionAndScaleTo(float aResolution,
                                               ResolutionChangeOrigin aOrigin) {
   MOZ_ASSERT(mPresShell);

layout/base/GeckoMVMContext.h

@@ -50,6 +50,7 @@ class GeckoMVMContext final : public MVMContext {
   bool AllowZoomingForDocument() const override;
   bool IsInReaderMode() const override;
   bool IsDocumentLoading() const override;
+  bool IsDocumentFullscreen() const override;
 
   void SetResolutionAndScaleTo(float aResolution,
                                ResolutionChangeOrigin aOrigin) override;

layout/base/MVMContext.h

@@ -57,6 +57,7 @@ class MVMContext {
   virtual bool AllowZoomingForDocument() const = 0;
   virtual bool IsInReaderMode() const = 0;
   virtual bool IsDocumentLoading() const = 0;
+  virtual bool IsDocumentFullscreen() const = 0;
 
   virtual void SetResolutionAndScaleTo(float aResolution,
                                        ResolutionChangeOrigin aOrigin) = 0;

layout/base/MobileViewportManager.cpp

@@ -352,7 +352,7 @@ void MobileViewportManager::UpdateResolutionForViewportSizeChange(
   //    viewport tag is added or removed)
   // 4. neither screen size nor CSS viewport changes
 
-  if (!aDisplayWidthChangeRatio) {
+  if (!aDisplayWidthChangeRatio || mContext->IsDocumentFullscreen()) {
     UpdateVisualViewportSize(zoom);
     return;
   }