Add ramdisk image sdk trait to cc_library_headers

Allows an sdk to require that a cc_library_headers module provides a
ramdisk image variant for the prebuilt.

Previously, "ramdisk_available: true" would be set in the generated
prebuilt snapshot for any sdk member that specified
"ramdisk_available: true" in the source module. This change will only
add that setting to the snapshot if the ramdisk image variant trait
was explicitly requested for a member.

Bug: 195754365
Test: m nothing
Change-Id: I21e0dd02d380beabf228a72c463fcc603c77d87f
diff --git a/cc/library_sdk_member.go b/cc/library_sdk_member.go
index a28ccd0..8988de2 100644
--- a/cc/library_sdk_member.go
+++ b/cc/library_sdk_member.go
@@ -134,6 +134,16 @@
 				targets:         targets,
 			})
 
+			// If required add additional dependencies on the image:ramdisk variants.
+			if ctx.RequiresTrait(lib, ramdiskImageRequiredSdkTrait) {
+				memberDependencies = append(memberDependencies, memberDependency{
+					imageVariations: []blueprint.Variation{{Mutator: "image", Variation: android.RamdiskVariation}},
+					// Only add a dependency on the first target as that is the only one which will have an
+					// image:ramdisk variant.
+					targets: targets[:1],
+				})
+			}
+
 			// If required add additional dependencies on the image:recovery variants.
 			if ctx.RequiresTrait(lib, recoveryImageRequiredSdkTrait) {
 				memberDependencies = append(memberDependencies, memberDependency{
@@ -199,6 +209,10 @@
 		pbm.AddProperty("native_bridge_supported", true)
 	}
 
+	if ctx.RequiresTrait(ramdiskImageRequiredSdkTrait) {
+		pbm.AddProperty("ramdisk_available", true)
+	}
+
 	if ctx.RequiresTrait(recoveryImageRequiredSdkTrait) {
 		pbm.AddProperty("recovery_available", true)
 	}