Make 'make docs' work on OpenJDK 9 toolchain.

OpenJDK 9's javadoc tool doesn't support the -bootclasspath
command line option, even with -source 1.8.

Instead, under OpenJDK 9, javadoc needs to be passed a
--patch-module argument to tell it the location of the
classes patching packages from java.* modules.

The source files in libcore/{dalvik,libart,luni,ojluni} and
external/icu/android_icu4j that go into PRIVATE_BOOTCLASSPATH
patch packages from the modules java.base, java.desktop,
java.logging, java.prefs, java.sql, jdk.net, and
jdk.unsupported. However, this CL takes the simpler approach
of placing them all in java.base, which appears to work for
the purposes of the javadoc run.

Test: Ran the following both on OpenJDK 8 toolchain and on
      OpenJDK 9 (with EXPERIMENTAL_USE_OPENJDK9=true):
      rm -rf out/target/common/docs/ && make docs
Test: Compared (via meld) the contents of out/target/common/docs
      for the two toolchains (there were some differences, see bug).
Bug: 62049770

Change-Id: If3dd927477ca32dab7ffb528350de872e1017184

core/droiddoc.mk

@@ -166,6 +166,10 @@ endif
 # TODO: not clear if this is used any more
 $(full_target): PRIVATE_LOCAL_PATH := $(LOCAL_PATH)
 
+# TODO(tobiast): Clean this up once we move to -source 1.9.
+# OpenJDK 9 does not have the concept of a "boot classpath" so we should
+# then rename PRIVATE_BOOTCLASSPATH to PRIVATE_MODULE or similar. For now,
+# keep -bootclasspath here since it works in combination with -source 1.8.
 $(full_target): \
         $(full_src_files) \
         $(droiddoc_templates) \
@@ -210,6 +214,18 @@ else
 ## standard doclet only
 ##
 ##
+
+ifneq ($(EXPERIMENTAL_USE_OPENJDK9),)
+# For OpenJDK 9 we use --patch-module to define the core libraries code.
+# TODO(tobiast): Reorganize this when adding proper support for OpenJDK 9
+# modules. Here we treat all code in core libraries as being in java.base
+# to work around the OpenJDK 9 module system. http://b/62049770
+$(full_target): PRIVATE_BOOTCLASSPATH_ARG := --patch-module=java.base=$(PRIVATE_BOOTCLASSPATH)
+else
+# For OpenJDK 8 we can use -bootclasspath to define the core libraries code.
+$(full_target): PRIVATE_BOOTCLASSPATH_ARG := $(addprefix -bootclasspath ,$(PRIVATE_BOOTCLASSPATH))
+endif
+
 $(full_target): $(full_src_files) $(full_java_lib_deps)
 	@echo Docs javadoc: $(PRIVATE_OUT_DIR)
 	@mkdir -p $(dir $@)
@@ -225,7 +241,7 @@ $(full_target): $(full_src_files) $(full_java_lib_deps)
                 -Xdoclint:none \
                 $(PRIVATE_PROFILING_OPTIONS) \
                 $(addprefix -classpath ,$(PRIVATE_CLASSPATH)) \
-                $(addprefix -bootclasspath ,$(PRIVATE_BOOTCLASSPATH)) \
+                $(PRIVATE_BOOTCLASSPATH_ARG) \
                 -sourcepath $(PRIVATE_SOURCE_PATH)$(addprefix :,$(PRIVATE_CLASSPATH)) \
                 -d $(PRIVATE_OUT_DIR) \
                 -quiet \