Bug 1859680 - Reject RecvFindImageText() messages on unsupported platforms. r=gregtatum

Also, avoid calling SendFindImageText() on unsupported platforms, so that
test_image_recognition_unsupported.html will pass.

Differential Revision: https://phabricator.services.mozilla.com/D191678

dom/ipc/ContentParent.cpp

@@ -5219,6 +5219,11 @@ mozilla::ipc::IPCResult ContentParent::RecvCopyFavicon(
 mozilla::ipc::IPCResult ContentParent::RecvFindImageText(
     IPCImage&& aImage, nsTArray<nsCString>&& aLanguages,
     FindImageTextResolver&& aResolver) {
+  if (!TextRecognition::IsSupported() ||
+      !Preferences::GetBool("dom.text-recognition.enabled")) {
+    return IPC_FAIL(this, "Text recognition not available.");
+  }
+
   RefPtr<DataSourceSurface> surf =
       nsContentUtils::IPCImageToSurface(std::move(aImage));
   if (!surf) {

widget/TextRecognition.cpp

@@ -35,6 +35,11 @@ auto TextRecognition::FindText(imgIContainer& aImage,
 auto TextRecognition::FindText(gfx::DataSourceSurface& aSurface,
                                const nsTArray<nsCString>& aLanguages)
     -> RefPtr<NativePromise> {
+  if (!IsSupported()) {
+    return NativePromise::CreateAndReject("Text recognition not available"_ns,
+                                          __func__);
+  }
+
   if (XRE_IsContentProcess()) {
     auto* contentChild = ContentChild::GetSingleton();
     auto image = nsContentUtils::SurfaceToIPCImage(aSurface);
@@ -108,10 +113,7 @@ void TextRecognition::FillShadow(ShadowRoot& aShadow,
 auto TextRecognition::DoFindText(gfx::DataSourceSurface&,
                                  const nsTArray<nsCString>&)
     -> RefPtr<NativePromise> {
-  MOZ_RELEASE_ASSERT(XRE_IsParentProcess(),
-                     "This should only run in the parent process");
-  return NativePromise::CreateAndReject("Text recognition not available"_ns,
-                                        __func__);
+  MOZ_CRASH("DoFindText is not implemented on this platform");
 }
 #endif