SurfaceControl: Add setDropInputMode api

Introduces an API to drop input events on this SurfaceControl. This
policy will be inherited by its children. The caller must hold the
ACCESS_SURFACE_FLINGER permission.

Options include:
ALL: SurfaceControl and its children will not receive any
input regardless of whether it has a valid input channel.
OBSCURED: SurfaceControl and its children will not
receive any input if the layer is obscured, cropped by its parent or
translucent.

These policies are used to enable features that allow for a less trusted
interaction model between apps. See the bug for more details.

Test: atest libgui_test InputDispatcherDropInputFeatureTest
Bug:197364677

Change-Id: I443741d5ab51a45d37fb865f11c433c436d96c1e
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index ef6f115..d549fe9 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -135,6 +135,7 @@
     mDrawingState.postTime = -1;
     mDrawingState.destinationFrame.makeInvalid();
     mDrawingState.isTrustedOverlay = false;
+    mDrawingState.dropInputMode = gui::DropInputMode::NONE;
 
     if (args.flags & ISurfaceComposerClient::eNoColorFill) {
         // Set an invalid color so there is no color fill.
@@ -2541,6 +2542,14 @@
     return handle->owner;
 }
 
+bool Layer::setDropInputMode(gui::DropInputMode mode) {
+    if (mDrawingState.dropInputMode == mode) {
+        return false;
+    }
+    mDrawingState.dropInputMode = mode;
+    return true;
+}
+
 // ---------------------------------------------------------------------------
 
 std::ostream& operator<<(std::ostream& stream, const Layer::FrameRate& rate) {