Pass OpenJDK 8's bootclasspath for host tools targeting <= 1.8.

Follow the Make change in I9b6081edfdd2c3e9a450ae8a39c4e32c3d2cda92
to explicitly pass the OpenJDK 8 bootclasspath when targeting <= 1.8.

Bug: 70862583
Test: java_test.go
Test: javap -c -p out/soong/.intermediates/external/guava/guava/linux_glibc_common/javac/classes/com/google/common/hash/AbstractStreamingHashFunction\$AbstractStreamingHasher.class  | grep ByteBuffer.flip
      shows java/nio/Buffer return type in signature.

Change-Id: Ief66bbf6e3a4220b3afb2e02009bd0157d4c7fae

java/java.go

@@ -597,6 +597,29 @@ func (j *Module) collectBuilderFlags(ctx android.ModuleContext, deps deps) javaB
 	// classpath
 	flags.bootClasspath.AddPaths(deps.bootClasspath)
 	flags.classpath.AddPaths(deps.classpath)
+
+	if len(flags.bootClasspath) == 0 && ctx.Host() && !ctx.Config().TargetOpenJDK9() &&
+		!Bool(j.properties.No_standard_libs) &&
+		inList(flags.javaVersion, []string{"1.6", "1.7", "1.8"}) {
+		// Give host-side tools a version of OpenJDK's standard libraries
+		// close to what they're targeting. As of Dec 2017, AOSP is only
+		// bundling OpenJDK 8 and 9, so nothing < 8 is available.
+		//
+		// When building with OpenJDK 8, the following should have no
+		// effect since those jars would be available by default.
+		//
+		// When building with OpenJDK 9 but targeting a version < 1.8,
+		// putting them on the bootclasspath means that:
+		// a) code can't (accidentally) refer to OpenJDK 9 specific APIs
+		// b) references to existing APIs are not reinterpreted in an
+		//    OpenJDK 9-specific way, eg. calls to subclasses of
+		//    java.nio.Buffer as in http://b/70862583
+		java8Home := ctx.Config().Getenv("ANDROID_JAVA8_HOME")
+		flags.bootClasspath = append(flags.bootClasspath,
+			android.PathForSource(ctx, java8Home, "jre/lib/jce.jar"),
+			android.PathForSource(ctx, java8Home, "jre/lib/rt.jar"))
+	}
+
 	// systemModules
 	if deps.systemModules != nil {
 		flags.systemModules = append(flags.systemModules, deps.systemModules)

java/java_test.go

@@ -53,6 +53,12 @@ func TestMain(m *testing.M) {
 }
 
 func testConfig(env map[string]string) android.Config {
+	if env == nil {
+		env = make(map[string]string)
+	}
+	if env["ANDROID_JAVA8_HOME"] == "" {
+		env["ANDROID_JAVA8_HOME"] = "jdk8"
+	}
 	return android.TestArchConfig(buildDir, env)
 
 }
@@ -150,6 +156,9 @@ func testContext(config android.Config, bp string,
 		"build/target/product/security/testkey": nil,
 
 		"build/soong/scripts/jar-wrapper.sh": nil,
+
+		"jdk8/jre/lib/jce.jar": nil,
+		"jdk8/jre/lib/rt.jar":  nil,
 	}
 
 	for k, v := range fs {
@@ -368,6 +377,7 @@ var classpathTestcases = []struct {
 		moduleType:    "java_library_host",
 		properties:    ``,
 		host:          android.Host,
+		bootclasspath: []string{"jdk8/jre/lib/jce.jar", "jdk8/jre/lib/rt.jar"},
 		classpath:     []string{},
 	},
 	{
@@ -383,6 +393,7 @@ var classpathTestcases = []struct {
 		host:          android.Host,
 		properties:    `host_supported: true,`,
 		classpath:     []string{},
+		bootclasspath: []string{"jdk8/jre/lib/jce.jar", "jdk8/jre/lib/rt.jar"},
 	},
 	{
 		name:       "host supported nostdlib",