Enforce clang-format for c-like sources on Travis

.travis.yml

@@ -6,3 +6,4 @@ before_script:
 script:
   - ./travis/build.sh
   - ./travis/test.sh
+  - ./travis/format.sh

travis/format.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+echo "Checking formatting..."
+
+case "$(uname -s)" in
+  Darwin)
+    OS="mac-x64"
+    ;;
+  Linux)
+    OS="linux-x64"
+    ;;
+  *)
+    echo "Unknown operating system."
+    exit -1
+    ;;
+esac
+
+CLANG_FORMAT="buildtools/$OS/clang/bin/clang-format"
+$CLANG_FORMAT --version
+
+FILES="$(find flutter/ -name '*.cpp' -or -name '*.h' -or -name '*.c' -or -name '*.cc' -or -name '*.m' -or -name '*.mm')"
+
+FAILED_CHECKS=0
+for FILE in $FILES; do
+  RESULT="$(diff -u "$FILE" <($CLANG_FORMAT --style=file "$FILE"))"
+  if ! [ -z "$RESULT" ]; then
+    echo "$RESULT"
+    FAILED_CHECKS=$(($counter+1))
+  fi
+done
+
+if [ $FAILED_CHECKS -ne 0 ]; then
+  echo "Some files are formatted incorrectly. To fix, apply diffs from above."
+fi
+
+exit $FAILED_CHECKS