Add debug ramdisk variant.

A module will be installed to /debug_ramdisk if debug_ramdisk is set to
true.

This is a reland of f84e9c05e2, with a fix
that removes /first_stage_ramdisk.

Bug: 184004542
Test: soong test
Change-Id: I739de63cfec6b0fec5a90f7c4741fc4d884d209c

android/image.go

@@ -30,6 +30,10 @@ type ImageInterface interface {
 	// vendor ramdisk partition).
 	VendorRamdiskVariantNeeded(ctx BaseModuleContext) bool
 
+	// DebugRamdiskVariantNeeded should return true if the module needs a debug ramdisk variant (installed on the
+	// debug ramdisk partition: $(PRODUCT_OUT)/debug_ramdisk).
+	DebugRamdiskVariantNeeded(ctx BaseModuleContext) bool
+
 	// RecoveryVariantNeeded should return true if the module needs a recovery variant (installed on the
 	// recovery partition).
 	RecoveryVariantNeeded(ctx BaseModuleContext) bool
@@ -60,6 +64,9 @@ const (
 
 	// VendorRamdiskVariation means a module to be installed to vendor ramdisk image.
 	VendorRamdiskVariation string = "vendor_ramdisk"
+
+	// DebugRamdiskVariation means a module to be installed to debug ramdisk image.
+	DebugRamdiskVariation string = "debug_ramdisk"
 )
 
 // imageMutator creates variants for modules that implement the ImageInterface that
@@ -83,6 +90,9 @@ func imageMutator(ctx BottomUpMutatorContext) {
 		if m.VendorRamdiskVariantNeeded(ctx) {
 			variations = append(variations, VendorRamdiskVariation)
 		}
+		if m.DebugRamdiskVariantNeeded(ctx) {
+			variations = append(variations, DebugRamdiskVariation)
+		}
 		if m.RecoveryVariantNeeded(ctx) {
 			variations = append(variations, RecoveryVariation)
 		}