Use exact version of NDK needed by presubmit in Github Actions

It is required to install ninja manually due to it not being included in
the virtual env provided by Github Actions runner.

See actions/runner-images#741

In order for Ninja to be visible to CMake during NDK builds, it must be
installed in the same subdirectory, so for now it is symlinked on Linux
builds. See b/206099937

Fixes: 216535050
Test: Github CI
Change-Id: I1a741b1765822f0004adc3985b7babc8022046a5

.github/workflows/presubmit.yml

@@ -164,12 +164,31 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: "11"
+      # Required for CMake when building workmanager.
+      - name: "Install Ninja"
+        run: |
+          set -x
+          if [ "$RUNNER_OS" == "Linux" ]; then
+            sudo apt-get install ninja-build
+          elif [ "$RUNNER_OS" == "macOS" ]; then
+            brew install ninja
+          elif [ "$RUNNER_OS" == "Windows" ]; then
+            choco install ninja
+          else
+            echo "Failed to install ninja due to unsupport OS: $RUNNER_OS"
+            exit 1
+          fi
+          # See b/206099937. Hack needed to make ninja visible to cmake during NDK builds
+          if [ ! -e "/usr/local/bin/ninja" ]; then
+            ln -s "/usr/bin/ninja" "/usr/local/bin/ninja"
+          fi
 
       - name: "Set environment variables"
         shell: bash
         run: |
           set -x
           echo "DIST_DIR=$HOME/dist" >> $GITHUB_ENV
+          echo "ANDROID_NDK_ROOT=$ANDROID_SDK_ROOT/ndk/23.1.7779620" >> $GITHUB_ENV
       # gradle action loads the dependencies cache only on the first run based on arguments.
       # to control it, we explicitly invoke it once which makes it load the dependencies cache with the parameters
       # we control