Auto accept android license on build machines.

Every time the android version that is used changes we need to update the license hash.

android/build.gradle

@@ -184,6 +184,47 @@ ext {
     moduleGroupId = 'com.facebook.react'
 }
 
+// If Android SDK is not installed, accept its license so that it
+// is automatically downloaded.
+afterEvaluate { project ->
+    // Either the environment variable ANDROID_HOME or the property sdk.dir in
+    // local.properties identifies where Android SDK is installed.
+    def androidHome = System.env.ANDROID_HOME
+    if (!androidHome) {
+        // ANDROID_HOME is not set. Is sdk.dir set?
+        def file = file("${project.rootDir}/local.properties")
+        def props = new Properties()
+        if (file.canRead()) {
+            file.withInputStream {
+                props.load(it)
+                androidHome = props.'sdk.dir'
+            }
+        }
+        if (!androidHome && (!file.exists() || file.canWrite())) {
+            // Neither ANDROID_HOME nor sdk.dir is set. Set sdk.dir (because
+            // environment variables cannot be set).
+            props.'sdk.dir' = "${project.buildDir}/android-sdk".toString()
+            file.withOutputStream {
+                props.store(it, null)
+                androidHome = props.'sdk.dir'
+            }
+        }
+    }
+    // If the license is not accepted, accept it so that automatic downloading
+    // kicks in.
+    if (androidHome) {
+        def dir = file("${androidHome}/licenses")
+        dir.mkdirs()
+        def file = file("${dir.path}/android-sdk-license")
+        if (!file.exists()) {
+            file.withWriter {
+                def hash = 'd56f5187479451eabf01fb78af6dfcb131a6481e'
+                it.write(hash, 0, hash.length())
+            }
+        }
+    }
+}
+
 // Force the version of the Android build tools we have chosen on all
 // subprojects. The forcing was introduced for react-native and the third-party
 // modules that we utilize such as react-native-background-timer.