Require Android SDK copy of CMake to build Vulkan on Android.

platform_tools/android/bin/android_setup.sh

Index: platform_tools/android/bin/android_setup.sh
diff --git a/platform_tools/android/bin/android_setup.sh b/platform_tools/android/bin/android_setup.sh
index 503ee023e724651857aac811c9dfc1d933d0bc2b..f242bfa51bd8be50639013a256df010f504ce191 100755
--- a/platform_tools/android/bin/android_setup.sh
+++ b/platform_tools/android/bin/android_setup.sh
@@ -52,10 +52,6 @@ if [ "$USE_CLANG" == "true" ]; then
   export GYP_DEFINES="skia_clang_build=1 $GYP_DEFINES"
 fi
 
-if [ "$SKIA_VULKAN" == "true" ]; then
-  export GYP_DEFINES="skia_vulkan=1 $GYP_DEFINES"
-fi
-
 function verbose {
   if [[ -n $VERBOSE ]]; then
     echo $@
@@ -89,6 +85,17 @@ if [ -z "$ANDROID_HOME" ]; then
   exportVar ANDROID_HOME $ANDROID_SDK_ROOT
 fi
 
+if [ "$SKIA_VULKAN" == "true" ]; then
+  export GYP_DEFINES="skia_vulkan=1 $GYP_DEFINES"
+  # add cmake from the SDK to your path if it doesn't exist
+  if [ ! -d "${ANDROID_SDK_ROOT}/cmake" ]; then
+     echo "The Android SDK Tools version of CMake is required to build Vulkan. ${ANDROID_SDK_ROOT}/cmake"
+     exit 1
+  else
+    export PATH=${ANDROID_SDK_ROOT}/cmake/bin:$PATH
+  fi
+fi
+
 # Helper function to configure the GYP defines to the appropriate values
 # based on the target device.
 setup_device() {