Prevent apex from using preferred prebuilt_boot_image

Bug: 177892522
Test: m nothing
Change-Id: I8530ffa4c5123f6055a6ca25421c17bb6fc037f0

apex/apex.go

@@ -567,7 +567,7 @@ var (
 	certificateTag  = dependencyTag{name: "certificate"}
 	executableTag   = dependencyTag{name: "executable", payload: true}
 	fsTag           = dependencyTag{name: "filesystem", payload: true}
-	bootImageTag    = dependencyTag{name: "bootImage", payload: true}
+	bootImageTag    = dependencyTag{name: "bootImage", payload: true, sourceOnly: true}
 	compatConfigTag = dependencyTag{name: "compatConfig", payload: true, sourceOnly: true}
 	javaLibTag      = dependencyTag{name: "javaLib", payload: true}
 	jniLibTag       = dependencyTag{name: "jniLib", payload: true}

apex/boot_image_test.go

@@ -190,6 +190,16 @@ func TestBootImageInApex(t *testing.T) {
 				"myapex",
 			],
 		}
+
+		// Make sure that a preferred prebuilt doesn't affect the apex.
+		prebuilt_boot_image {
+			name: "mybootimage",
+			image_name: "boot",
+			prefer: true,
+			apex_available: [
+				"myapex",
+			],
+		}
 	`)
 
 	ensureExactContents(t, result.TestContext, "myapex", "android_common_myapex_image", []string{
@@ -206,6 +216,11 @@ func TestBootImageInApex(t *testing.T) {
 		"javalib/arm64/boot-foo.oat",
 		"javalib/arm64/boot-foo.vdex",
 	})
+
+	java.CheckModuleDependencies(t, result.TestContext, "myapex", "android_common_myapex_image", []string{
+		`myapex.key`,
+		`mybootimage`,
+	})
 }
 
 // TODO(b/177892522) - add test for host apex.