android: Update gradle layer build to use cmake
diff --git a/build-android/cmake/README.md b/build-android/cmake/README.md
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+Build Validation Layers with Android CMake
+=========================================
+Gradle's CMake library project in this directory builds layers into AAR;
+the project could be directly added into application's gradle projects
+
+Pre-requirements
+----------------
+Build ShaderC binary
+- Building from Github Repo source
+1. cd android-build
+2. ./update_external_sources_android.sh
+3. ./android-generate.sh
+
+Extra Steps if building from NDK's source tree
+```
+ cd ${your ANDROID_NDK_ROOT}/sources/third_party/shaderc
+ ndk-build APP_ABI=armeabi-v7a APP_STL=gnustl_static NDK_TOOLCHAIN_VERSION=clang NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=Android.mk libshaderc_combined
+```
+
+Adding layer module into Android Studio application project
+--------------------------------------------------------
+1. app's settings.gradle, add
+```java
+ include ':layerLib'
+ project(':layerLib').projectDir = new File('/path/to/cmake/layerlib')
+```
+2. app's build.gradle:
+```java
+dependencies {
+ // force debug layer lib for packing
+ compile project(path: ':layerlib', configuration: 'debug')
+}
+```
+BUILD_IN_NDK variable in layerlib/CMakeLists.txt could detect whether the source is
+from NDK or github repo clone, and would configure the file paths accordingly
+
+Tested
+-----
+ Build on Mac OS, Nexus 5X test phone. Equvilaent build scripts for Windows OS are at the same directory.
+