Allow translation of unknown source language page on desktop only

Bug: 1139799
Change-Id: I23a4c92316b47b1d95240702a758e799a00d05a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488368
Commit-Queue: Anthony Cui <cuianthony@chromium.org>
Reviewed-by: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819495}

components/translate/core/browser/translate_manager.cc

@@ -213,9 +213,14 @@ bool TranslateManager::CanManuallyTranslate() {
     return false;
 
   const std::string source_language = language_state_.original_language();
-  if (source_language.empty() ||
-      source_language == translate::kUnknownLanguageCode)
+  if (source_language.empty())
     return false;
+  // Translation of unknown source language pages is supported on desktop
+  // platforms, but not mobile.
+#if defined(OS_ANDROID) || defined(OS_IOS)
+  if (source_language == translate::kUnknownLanguageCode)
+    return false;
+#endif
 
   std::unique_ptr<TranslatePrefs> translate_prefs(
       translate_client_->GetTranslatePrefs());

components/translate/core/browser/translate_manager_unittest.cc

@@ -1019,7 +1019,13 @@ TEST_F(TranslateManagerTest, CanManuallyTranslate_UndefinedSourceLanguage) {
   translate_manager_->GetLanguageState()->LanguageDetermined(
       translate::kUnknownLanguageCode, true);
 
+  // Translation of unknown source language pages is supported on desktop
+  // platforms, but not mobile.
+#if defined(OS_ANDROID) || defined(OS_IOS)
   EXPECT_FALSE(translate_manager_->CanManuallyTranslate());
+#else
+  EXPECT_TRUE(translate_manager_->CanManuallyTranslate());
+#endif
 }
 
 TEST_F(TranslateManagerTest, PredefinedTargetLanguage) {