Touch emulator: enables double tap support for pages similar to Chrome on Android.

content/browser/renderer_host/input/touch_emulator.cc

Index: content/browser/renderer_host/input/touch_emulator.cc
diff --git a/content/browser/renderer_host/input/touch_emulator.cc b/content/browser/renderer_host/input/touch_emulator.cc
index 8592bd2031c3f9dd0a0dadde0f8ef4717f91cb96..be24b9d2c2c377acd7422788dcef575cd86a9cee 100644
--- a/content/browser/renderer_host/input/touch_emulator.cc
+++ b/content/browser/renderer_host/input/touch_emulator.cc
@@ -47,6 +47,7 @@ TouchEmulator::TouchEmulator(TouchEmulatorClient* client)
     : client_(client),
       gesture_provider_config_type_(
           ui::GestureProviderConfigType::CURRENT_PLATFORM),
+      double_tap_enabled_(true),
       emulated_stream_active_sequence_count_(0),
       native_stream_active_sequence_count_(0) {
   DCHECK(client_);
@@ -92,9 +93,7 @@ void TouchEmulator::Enable(ui::GestureProviderConfigType config_type) {
         GetEmulatorGestureProviderConfig(config_type), this));
     // TODO(dgozman): Use synthetic secondary touch to support multi-touch.
     gesture_provider_->SetMultiTouchZoomSupportEnabled(false);
-    // TODO(dgozman): Enable double tap if requested by the renderer.
-    // TODO(dgozman): Don't break double-tap-based pinch with shift handling.
-    gesture_provider_->SetDoubleTapSupportForPlatformEnabled(false);
+    gesture_provider_->SetDoubleTapSupportForPageEnabled(double_tap_enabled_);

[jdduke (slow), 2015/01/22 16:28:27]

Hmm, is it intentional that we could support double-tap here for desktop
platforms, even when desktop platforms never support it in practice? Should we
|SetDoubleTapSupportForPlatformEnabled| depending on mobile/desktop config?
Alternatively we could have have double_tap_support_for_platform be a parameter
on GestureProvider::Config, and have its factory set the right value.

[dgozman, 2015/01/22 17:04:37]

I thought that config does already contain
SetDoubleTapSupportForPlatformEnabled. That seems like a right place for it.

[jdduke (slow), 2015/01/22 17:09:36]

Do you want to do that in this patch? Or I can quickly whip up a patch to do
that and land before we land this patch?

   }
   UpdateCursor();
 }
@@ -109,6 +108,12 @@ void TouchEmulator::Disable() {
   ResetState();
 }
 
+void TouchEmulator::SetDoubleTapSupportForPageEnabled(bool enabled) {
+  double_tap_enabled_ = enabled;
+  if (gesture_provider_)
+    gesture_provider_->SetDoubleTapSupportForPageEnabled(enabled);
+}
+
 gfx::SizeF TouchEmulator::InitCursorFromResource(
     WebCursor* cursor, float scale, int resource_id) {
   gfx::Image& cursor_image =