Switch all remaining android builders to ninja

build/android/envsetup_functions.sh

Index: build/android/envsetup_functions.sh
diff --git a/build/android/envsetup_functions.sh b/build/android/envsetup_functions.sh
index 08c3a165ac14922c8ee57d33d7c0d8de3149bfbb..50eb3cc47071dae003abeef2607534d44e7e9eed 100755
--- a/build/android/envsetup_functions.sh
+++ b/build/android/envsetup_functions.sh
@@ -134,8 +134,15 @@ common_vars_defines() {
 common_gyp_vars() {
   export GYP_DEFINES="${DEFINES}"
 
-  # Set GYP_GENERATORS to make-android if it's currently unset or null.
-  export GYP_GENERATORS="${GYP_GENERATORS:-make-android}"
+  # Set GYP_GENERATORS to ninja if it's currently unset or null.
+  if [ -z $GYP_GENERATORS ]; then
+    echo "Defaulting GYP_GENERATORS to ninja."
+    GYP_GENERATORS=ninja
+  elif [ "$GYP_GENERATORS" != "ninja" ]; then
+    echo "Warning: GYP_GENERATORS set to '$GYP_GENERATORS'."
+    echo "Only GYP_GENERATORS=ninja has continuous coverage."
+  fi
+  export GYP_GENERATORS
 
   # Use our All target as the default
   export GYP_GENERATOR_FLAGS="${GYP_GENERATOR_FLAGS} default_target=All"