Add streaming proto option to the build system.

Test: make w/ other prereq changes
Change-Id: Ie8711878e244074a9a3c128467eeb4908c2ef008
diff --git a/core/definitions.mk b/core/definitions.mk
index ed8f26d..52e28ce 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1150,6 +1150,7 @@
 ###########################################################
 ## Commands for running protoc to compile .proto into .java
 ###########################################################
+# PATH contains HOST_OUT_EXECUTABLES to allow protoc-gen-* plugins
 
 define transform-proto-to-java
 @mkdir -p $(dir $@)
@@ -1157,6 +1158,7 @@
 @rm -rf $(PRIVATE_PROTO_JAVA_OUTPUT_DIR)
 @mkdir -p $(PRIVATE_PROTO_JAVA_OUTPUT_DIR)
 $(hide) for f in $(PRIVATE_PROTO_SRC_FILES); do \
+        PATH=$$PATH:$(HOST_OUT_EXECUTABLES) \
         $(PROTOC) \
         $(addprefix --proto_path=, $(PRIVATE_PROTO_INCLUDES)) \
         $(PRIVATE_PROTO_JAVA_OUTPUT_OPTION)="$(PRIVATE_PROTO_JAVA_OUTPUT_PARAMS):$(PRIVATE_PROTO_JAVA_OUTPUT_DIR)" \
@@ -1169,10 +1171,14 @@
 ######################################################################
 ## Commands for running protoc to compile .proto into .pb.cc (or.pb.c) and .pb.h
 ######################################################################
+# PATH contains HOST_OUT_EXECUTABLES to allow protoc-gen-* plugins
+
 define transform-proto-to-cc
 @echo "Protoc: $@ <= $<"
 @mkdir -p $(dir $@)
-$(hide) $(PROTOC) \
+$(hide) \
+	PATH=$$PATH:$(HOST_OUT_EXECUTABLES) \
+	$(PROTOC) \
 	$(addprefix --proto_path=, $(PRIVATE_PROTO_INCLUDES)) \
 	$(PRIVATE_PROTOC_FLAGS) \
 	$<