Check Java formatting in format.sh (#16500)

Uses google-java-format, a tool that's already in place in
flutter/plugins. This should take care of minor style guide issues and
unresolved imports.

DEPS

@@ -436,6 +436,20 @@ deps = {
      'dep_type': 'cipd',
    },
 
+   'src/third_party/android_tools/google-java-format': {
+     'packages': [
+       {
+        'package': 'flutter/android/google-java-format',
+        'version': 'version:1.7-1'
+       }
+     ],
+     # We want to be able to format these as part of CI, and the CI step that
+     # checks formatting runs without downloading the rest of the Android build
+     # tooling. Therefore unlike all the other Android-related tools, we want to
+     # download this every time.
+     'dep_type': 'cipd',
+   },
+
   'src/third_party/android_tools/sdk/build-tools': {
      'packages': [
        {

ci/format.sh

@@ -30,7 +30,7 @@ CLANG_FORMAT="../buildtools/$OS/clang/bin/clang-format"
 $CLANG_FORMAT --version
 
 # Compute the diffs.
-FILETYPES="*.c *.cc *.cpp *.h *.m *.mm"
+CLANG_FILETYPES="*.c *.cc *.cpp *.h *.m *.mm"
 DIFF_OPTS="-U0 --no-color --name-only"
 
 if git remote get-url upstream >/dev/null 2>&1; then
@@ -42,10 +42,9 @@ fi;
 
 BASE_SHA="$(git fetch $UPSTREAM master > /dev/null 2>&1 && \
            (git merge-base --fork-point FETCH_HEAD HEAD || git merge-base FETCH_HEAD HEAD))"
-FILES_TO_CHECK="$(git diff $DIFF_OPTS $BASE_SHA -- $FILETYPES)"
-
+CLANG_FILES_TO_CHECK="$(git diff $DIFF_OPTS $BASE_SHA -- $CLANG_FILETYPES)"
 FAILED_CHECKS=0
-for f in $FILES_TO_CHECK; do
+for f in $CLANG_FILES_TO_CHECK; do
   set +e
   CUR_DIFF="$(diff -u "$f" <("$CLANG_FORMAT" --style=file "$f"))"
   set -e
@@ -55,6 +54,24 @@ for f in $FILES_TO_CHECK; do
   fi
 done
 
+GOOGLE_JAVA_FORMAT="../third_party/android_tools/google-java-format/google-java-format-1.7-all-deps.jar"
+if [[ -f "$GOOGLE_JAVA_FORMAT" && -f "$(which java)" ]]; then
+  java -jar "$GOOGLE_JAVA_FORMAT" --version 2>&1
+  JAVA_FILETYPES="*.java"
+  JAVA_FILES_TO_CHECK="$(git diff $DIFF_OPTS $BASE_SHA -- $JAVA_FILETYPES)"
+  for f in $JAVA_FILES_TO_CHECK; do
+    set +e
+    CUR_DIFF="$(diff -u "$f" <(java -jar "$GOOGLE_JAVA_FORMAT" "$f"))"
+    set -e
+    if [[ ! -z "$CUR_DIFF" ]]; then
+      echo "$CUR_DIFF"
+      FAILED_CHECKS=$(($FAILED_CHECKS+1))
+    fi
+  done
+else
+  echo "WARNING: Cannot find google-java-format, skipping Java file formatting!"
+fi
+
 if [[ $FAILED_CHECKS -ne 0 ]]; then
   echo ""
   echo "ERROR: Some files are formatted incorrectly. To fix, run \`./ci/format.sh | patch -p0\` from the flutter/engine/src/flutter directory."