Provide alternatives to adding ndk-build to $PATH

imagepipeline/build.gradle

@@ -16,7 +16,7 @@ dependencies {
     compile "com.android.support:support-v4:${SUPPORT_V4_VERSION}"
     compile "javax.annotation:javax.annotation-api:${ANNOTATION_API_VERSION}"
     compile project(':fbcore')
-    
+
     androidTestCompile "com.google.guava:guava:${GUAVA_VERSION}"
     androidTestCompile "junit:junit:${JUNIT_VERSION}"
     androidTestCompile "org.mockito:mockito-core:${MOCKITO_CORE_VERSION}"
@@ -125,11 +125,28 @@ task copyLibWebp(dependsOn: cloneWebp, type: Copy) {
     into "${nativemerge}/libwebp-0.4.2"
 }
 
+def getNdkBuildCommand() {
+    // we allow to provide full path to ndk-build tool
+    if (hasProperty('ndk.command')) {
+        return property('ndk.command')
+    }
+    // or just a path to the containing directiry
+    if (hasProperty('ndk.path')) {
+        def path = property('ndk.path')
+        if (!path.endsWith(File.separator)) {
+            path += File.separator
+        }
+        return path + 'ndk-build'
+    }
+    // if none of above is provided, we assume ndk-build is already in $PATH
+    return 'ndk-build'
+}
+
 def makeNdkTasks(String name) {
     task "ndk_build_$name"(type: Exec) {
         inputs.file("src/main/jni/$name")
         outputs.dir("$buildDir/$name")
-        commandLine 'ndk-build',
+        commandLine getNdkBuildCommand(),
             'NDK_APPLICATION_MK=../Application.mk',
             'NDK_OUT=' + temporaryDir,
             "NDK_LIBS_OUT=$buildDir/$name",
@@ -138,7 +155,7 @@ def makeNdkTasks(String name) {
     }
 
     task "ndk_clean_$name"(type: Exec) {
-        commandLine 'ndk-build',
+        commandLine getNdkBuildCommand(),
             'NDK_APPLICATION_MK=../Application.mk',
             'NDK_OUT=' + temporaryDir,
             "NDK_LIBS_OUT=$buildDir/$name",