Exclude Fabric from RN OSS by default

Summary:
This diff adds a new mechanism to enable or disable the build of Fabric in RN OSS

changelog: [internal] internal

Reviewed By: fkgozali

Differential Revision: D23084586

fbshipit-source-id: b7b0b842486392ec4ccb91ad1e6441ba3a1f48b2

ReactAndroid/build.gradle

@@ -33,6 +33,11 @@ def thirdPartyNdkDir = new File("$buildDir/third-party-ndk")
 //   - glog-0.3.5
 def dependenciesPath = System.getenv("REACT_NATIVE_DEPENDENCIES")
 
+// The 'USE_FABRIC' environment variable will build Fabric C++ code into the bundle
+// USE_FABRIC=false will build RN excluding fabric
+// USE_FABRIC=true will build RN including fabric
+def enableFabric = System.getenv("USE_FABRIC") ?: "false"
+
 // The Boost library is a very large download (>100MB).
 // If Boost is already present on your system, define the REACT_NATIVE_BOOST_PATH env variable
 // and the build will use that.
@@ -312,6 +317,7 @@ def buildReactNdkLib = tasks.register("buildReactNdkLib", Exec) {
             "THIRD_PARTY_NDK_DIR=$buildDir/third-party-ndk",
             "REACT_COMMON_DIR=$projectDir/../ReactCommon",
             "REACT_SRC_DIR=$projectDir/src/main/java/com/facebook/react",
+            "BUILD_FABRIC=$enableFabric",
             "-C", file("src/main/jni/react/jni").absolutePath,
             "--jobs", project.findProperty("jobs") ?: Runtime.runtime.availableProcessors()
     )

ReactAndroid/src/main/jni/react/jni/Android.mk

@@ -77,7 +77,7 @@ LOCAL_CFLAGS += -fexceptions -frtti -Wno-unused-lambda-capture
 LOCAL_LDLIBS += -landroid
 
 # The dynamic libraries (.so files) that this module depends on.
-LOCAL_SHARED_LIBRARIES := libreactnativeutilsjni libfolly_json libfb libfbjni libglog_init libyoga libfabricjni
+LOCAL_SHARED_LIBRARIES := libreactnativeutilsjni libfolly_json libfb libfbjni libglog_init libyoga
 
 # The static libraries (.a files) that this module depends on.
 LOCAL_STATIC_LIBRARIES := libreactnative libcallinvokerholder libruntimeexecutor
@@ -131,7 +131,10 @@ $(call import-module,runtimeexecutor)
 
 include $(REACT_SRC_DIR)/reactperflogger/jni/Android.mk
 include $(REACT_SRC_DIR)/turbomodule/core/jni/Android.mk
-include $(REACT_SRC_DIR)/fabric/jni/Android.mk
+
+ifeq ($(BUILD_FABRIC),true)
+  include $(REACT_SRC_DIR)/fabric/jni/Android.mk
+endif
 
 # TODO(ramanpreet):
 #   Why doesn't this import-module call generate a jscexecutor.so file?