[Impeller] Provisional iOS impeller flag-flip.

common/settings.h

@@ -14,6 +14,7 @@
 #include <string>
 #include <vector>
 
+#include "flutter/fml/build_config.h"
 #include "flutter/fml/closure.h"
 #include "flutter/fml/mapping.h"
 #include "flutter/fml/time/time_point.h"
@@ -210,7 +211,11 @@ struct Settings {
 
   // Enable the Impeller renderer on supported platforms. Ignored if Impeller is
   // not supported on the platform.
+#if FML_OS_IOS || FML_OS_IOS_SIMULATOR
+  bool enable_impeller = true;
+#else
   bool enable_impeller = false;
+#endif
 
   // Data set by platform-specific embedders for use in font initialization.
   uint32_t font_initialization_data = 0;

shell/common/switches.cc

@@ -443,8 +443,12 @@ Settings SettingsFromCommandLine(const fml::CommandLine& command_line) {
   settings.use_asset_fonts =
       !command_line.HasOption(FlagForSwitch(Switch::DisableAssetFonts));
 
-  settings.enable_impeller =
-      command_line.HasOption(FlagForSwitch(Switch::EnableImpeller));
+  std::string enable_impeller_value;
+  if (command_line.GetOptionValue(FlagForSwitch(Switch::EnableImpeller),
+                                  &enable_impeller_value)) {
+    settings.enable_impeller =
+        enable_impeller_value.empty() || "true" == enable_impeller_value;
+  }
 
   settings.enable_embedder_api =
       command_line.HasOption(FlagForSwitch(Switch::EnableEmbedderAPI));

testing/scenario_app/ios/Scenarios/Scenarios/Info.plist

@@ -41,5 +41,7 @@
 		<string>UIInterfaceOrientationLandscapeLeft</string>
 		<string>UIInterfaceOrientationLandscapeRight</string>
 	</array>
+	<key>FLTEnableImpeller</key>
+	<false/>
 </dict>
 </plist>