[android] - move example custom layer compilation to testapp

platform/android/MapboxGLAndroidSDKTestApp/build.gradle

@@ -17,6 +17,71 @@ android {
         targetCompatibility JavaVersion.VERSION_1_8
     }
 
+    defaultPublishConfig project.hasProperty("mapbox.buildtype") ? project.getProperty("mapbox.buildtype") : "debug"
+
+    // We sometimes want to invoke Gradle without building a native dependency, e.g. when we just want
+    // to invoke the Java tests. When we explicitly specify an ABI of 'none', no native dependencies are
+    // added. When another ABI is specified explicitly, we're just going to build that ABI. In all other
+    // cases, all ABIs are built.
+    //
+    // When invoking from the command line or to override the device default, set `-Pmapbox.abis=...` to
+    // only build the desired architectures.
+    //
+    // When building from Android Studio, gradle.properties sets `android.buildOnlyTargetAbi=true` so that
+    // only the architecture for the device you're running on gets built.
+    def abi = 'all'
+    if (!project.hasProperty('android.injected.invoked.from.ide') || project.hasProperty("mapbox.abis")) {
+        // Errors when the user invokes Gradle from the command line and didn't set mapbox.abis
+        abi = project.getProperty("mapbox.abis")
+    }
+
+    if (abi != 'none') {
+        externalNativeBuild {
+            cmake {
+                path "../../../CMakeLists.txt"
+                version "3.10.2"
+            }
+        }
+    }
+
+    // Allow determining the C++ STL we're using when building Mapbox GL.
+    def stl = 'c++_static'
+    if (project.hasProperty("mapbox.stl")) {
+        stl = project.getProperty("mapbox.stl")
+    }
+
+    defaultConfig {
+        if (abi != 'none') {
+            externalNativeBuild {
+                cmake {
+                    arguments "-DANDROID_TOOLCHAIN=clang"
+                    arguments "-DANDROID_STL=" + stl
+                    arguments "-DANDROID_CPP_FEATURES=exceptions"
+                    arguments "-DMBGL_PLATFORM=android"
+                    arguments "-DMASON_PLATFORM=android"
+                    arguments "-DNodeJS_EXECUTABLE=" + node
+                    arguments "-Dnpm_EXECUTABLE=" + npm
+
+                    // Enable ccache if the user has installed it.
+                    if (ccache?.trim()) {
+                        arguments "-DANDROID_CCACHE=" + ccache
+                    }
+
+                    cFlags "-Qunused-arguments"
+                    cppFlags "-Qunused-arguments"
+
+                    targets "example-custom-layer"
+
+                    if (abi != 'all') {
+                        abiFilters abi.split(' ')
+                    } else {
+                        abiFilters "armeabi-v7a", "x86", "arm64-v8a", "x86_64"
+                    }
+                }
+            }
+        }
+    }
+
     packagingOptions {
         exclude 'META-INF/LICENSE.txt'
         exclude 'META-INF/NOTICE.txt'