Support java compilation sharding for target side.

Add "LOCAL_JAVAC_SHARD_SIZE" to represent the number of java
source path entries in each shard.

Sharding is not allowed when "LOCAL_JAVAC_SHARD_SIZE" and
"LOCAL_JAR_PROCESSORS" are both enabled.

Limitation:
1. 0 <= LOCAL_JAVAC_SHARD_SIZE <= 8192
1. 0 < NUM(java_sources) <= 8192
2. 0 <= NUM(shards) <= 100

Performance Compare:
<Unsharded Build------------------------------------------------>
1. Build from clean state
rm -r -f out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/
&& time m
out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar

real	1m2.720s user	5m26.604s sys	0m39.552s

2. Incremental build
m out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar &&
touch frameworks/base/core/java/android/net/http/HttpResponseCache.java && time m
out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar

real	0m37.586s user	5m47.804s sys	0m50.388s

<Sharded Build-------------------------------------------------->
1. Build from clean state
rm -r -f out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/
&& time m
out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar

Javac Shard Size: 50----real	1m10.163s user	25m59.008s sys	1m58.460s
Javac Shard Size: 100---real	1m2.115s user	21m3.600s sys	1m15.964s
Javac Shard Size: 150---real	0m59.520s user	18m10.544s sys	1m12.628s
Javac Shard Size: 200---real	0m56.894s user	15m39.244s sys	1m11.608s
Javac Shard Size: 250---real	0m55.991s user	14m38.716s sys	1m2.292s
Javac Shard Size: 300---real	0m55.114s user	13m6.568s sys	1m8.200s
Javac Shard Size: 350---real	0m53.144s user	12m7.740s sys	1m3.836s
Javac Shard Size: 400---real	0m54.929s user	12m9.324s sys	1m4.340s
Javac Shard Size: 450---real	1m30.194s user	25m31.468s sys	1m52.416s
Javac Shard Size: 500---real	0m53.976s user	10m35.500s sys	0m55.160s

2. Incremental build
m out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar &&
touch frameworks/base/core/java/android/net/http/HttpResponseCache.java && time m
out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes-full-debug.jar

Javac Shard Size: 50-----real	0m16.322s user	1m8.648s sys	0m31.700s
Javac Shard Size: 100----real	0m16.163s user	1m22.932s sys	0m29.440s
Javac Shard Size: 150----real	0m16.611s user	1m37.828s sys	0m21.168s
Javac Shard Size: 200----real	0m16.936s user	1m49.248s sys	0m28.636s
Javac Shard Size: 250----real	0m17.509s user	1m54.944s sys	0m32.768s
Javac Shard Size: 300----real	0m18.868s user	1m54.088s sys	0m28.824s
Javac Shard Size: 350----real	0m17.629s user	1m54.108s sys	0m31.056s
Javac Shard Size: 400----real	0m18.658s user	2m7.712s sys	0m30.636s
Javac Shard Size: 450----real	0m18.874s user	2m8.808s sys	0m33.540s
Javac Shard Size: 500----real	0m19.432s user	2m24.400s sys	0m30.368s

time m nothing:
real 0m5.799s user 0m7.236s sys 0m3.068s

Test: m clean && m -j checkbuild
Bug: b/67424047
Change-Id: Id0766d2b7de7c4546d29bbc7f8a0dd0e4b9ad45b
diff --git a/core/definitions.mk b/core/definitions.mk
index cb0a6bb..1f9891e 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2205,6 +2205,17 @@
     @<(find $(1) -type f | sort | $(JAR_ARGS) $(1); echo "-C $(EMPTY_DIRECTORY) .")
 endef
 
+# append additional Java sources(resources/Proto sources, and etc) to $(1).
+define fetch-additional-java-source
+$(hide) if [ -d "$(PRIVATE_SOURCE_INTERMEDIATES_DIR)" ]; then \
+    find $(PRIVATE_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $(1); \
+fi
+$(if $(PRIVATE_HAS_PROTO_SOURCES), \
+    $(hide) find $(PRIVATE_PROTO_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $(1))
+$(if $(PRIVATE_HAS_RS_SOURCES), \
+    $(hide) find $(PRIVATE_RS_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $(1))
+endef
+
 # Some historical notes:
 # - below we write the list of java files to java-source-list to avoid argument
 #   list length problems with Cygwin
@@ -2214,16 +2225,20 @@
 @echo "$($(PRIVATE_PREFIX)DISPLAY) Java source list: $(PRIVATE_MODULE)"
 $(hide) rm -f $@
 $(call dump-words-to-file,$(sort $(PRIVATE_JAVA_SOURCES)),$@.tmp)
-$(hide) if [ -d "$(PRIVATE_SOURCE_INTERMEDIATES_DIR)" ]; then \
-    find $(PRIVATE_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $@.tmp; \
-fi
-$(if $(PRIVATE_HAS_PROTO_SOURCES), \
-    $(hide) find $(PRIVATE_PROTO_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $@.tmp)
-$(if $(PRIVATE_HAS_RS_SOURCES), \
-    $(hide) find $(PRIVATE_RS_SOURCE_INTERMEDIATES_DIR) -name '*.java' -and -not -name '.*' >> $@.tmp)
+$(call fetch-additional-java-source,$@.tmp)
 $(hide) tr ' ' '\n' < $@.tmp | $(NORMALIZE_PATH) | sort -u > $@
 endef
 
+# $(1): sharding number.
+# $(2): Java source files paths.
+define save-sharded-java-source-list
+$(java_source_list_file).shard.$(1): $(2) $$(NORMALIZE_PATH)
+	@echo "shard java source list: $$@"
+	rm -f $$@
+	$$(call dump-words-to-file,$(2),$$@.tmp)
+	$(hide) tr ' ' '\n' < $$@.tmp | $$(NORMALIZE_PATH) | sort -u > $$@
+endef
+
 # Common definition to invoke javac on the host and target.
 #
 # $(1): javac
@@ -2265,9 +2280,33 @@
 $(if $(PRIVATE_EXTRA_JAR_ARGS),$(call add-java-resources-to,$@))
 endef
 
-define transform-java-to-classes.jar
-@echo "$($(PRIVATE_PREFIX)DISPLAY) Java: $(PRIVATE_MODULE) ($(PRIVATE_CLASS_INTERMEDIATES_DIR))"
-$(call compile-java,$(TARGET_JAVAC),$(PRIVATE_ALL_JAVA_HEADER_LIBRARIES))
+# $(1): Javac output jar name.
+# $(2): Java source list file.
+# $(3): Java header libs.
+# $(4): Javac sharding number.
+# $(5): Javac sources deps (the arg may neeed $$ in case of containing '#')
+define create-classes-full-debug.jar
+$(1): PRIVATE_JAVACFLAGS := $$(LOCAL_JAVACFLAGS) $$(annotation_processor_flags)
+$(1): PRIVATE_JAR_EXCLUDE_FILES := $$(LOCAL_JAR_EXCLUDE_FILES)
+$(1): PRIVATE_JAR_PACKAGES := $$(LOCAL_JAR_PACKAGES)
+$(1): PRIVATE_JAR_EXCLUDE_PACKAGES := $$(LOCAL_JAR_EXCLUDE_PACKAGES)
+$(1): PRIVATE_DONT_DELETE_JAR_META_INF := $$(LOCAL_DONT_DELETE_JAR_META_INF)
+$(1): PRIVATE_JAVA_SOURCE_LIST := $(2)
+$(1): PRIVATE_ALL_JAVA_HEADER_LIBRARIES := $(3)
+$(1): PRIVATE_CLASS_INTERMEDIATES_DIR := $(intermediates.COMMON)/classes$(4)
+$(1): PRIVATE_ANNO_INTERMEDIATES_DIR := $(intermediates.COMMON)/anno$(4)
+$(1): \
+    $(2) \
+    $(3) \
+    $(5) \
+    $$(full_java_bootclasspath_libs) \
+    $$(layers_file) \
+    $$(annotation_processor_deps) \
+    $$(NORMALIZE_PATH) \
+    $$(JAR_ARGS) \
+    | $$(SOONG_JAVAC_WRAPPER)
+	@echo "Target Java: $$@ ($$(PRIVATE_CLASS_INTERMEDIATES_DIR))"
+	$$(call compile-java,$$(TARGET_JAVAC),$$(PRIVATE_ALL_JAVA_HEADER_LIBRARIES))
 endef
 
 define transform-java-to-header.jar