OSS: add gradle wrapper helper to prepare offline gradle caches

Summary:
This is to help build offline module caches for gradle builds.

allow-large-files

Reviewed By: hramos

Differential Revision: D7441450

fbshipit-source-id: 37ceb070223f0de06720f5c104ecfce2ad6cedfd

ReactAndroid/build.gradle

@@ -13,7 +13,8 @@ import org.apache.tools.ant.filters.ReplaceTokens
 // We then copy both the downloaded code and our custom makefiles and headers into third-party-ndk.
 // After that we build native code from src/main/jni with module path pointing at third-party-ndk.
 
-def downloadsDir = new File("$buildDir/downloads")
+def customDownloadsDir = System.getenv("REACT_NATIVE_DOWNLOADS_DIR")
+def downloadsDir = customDownloadsDir ? new File(customDownloadsDir) : new File("$buildDir/downloads")
 def thirdPartyNdkDir = new File("$buildDir/third-party-ndk")
 
 // You need to have following folders in this directory:
@@ -145,6 +146,16 @@ task prepareJSC(dependsOn: dependenciesPath ? [] : [downloadJSCHeaders]) << {
     }
 }
 
+task downloadNdkBuildDependencies {
+  if (!boostPath) {
+    dependsOn downloadBoost
+  }
+  dependsOn downloadDoubleConversion
+  dependsOn downloadFolly
+  dependsOn downloadGlog
+  dependsOn downloadJSCHeaders
+}
+
 def getNdkBuildName() {
     if (Os.isFamily(Os.FAMILY_WINDOWS)) {
         return "ndk-build.cmd"