Travis: upgrade the OS image from trusty to xenial. (#438)

* Use release binary of buildifier instead of building from source.
* Upgrade to clang-format 7.

Author: g-easy

.travis.yml

@@ -4,24 +4,16 @@ compiler: clang
 matrix:
   include:
     - os: linux
-      dist: trusty
-      sudo: false
       name: "check format"
       script: tools/travis/check_format.sh
     - os: linux
-      dist: trusty
-      sudo: false
       env: BAZEL_OS=linux
       script: tools/travis/build_bazel.sh
     - os: linux
-      dist: trusty
-      sudo: false
       compiler: gcc
       env: BAZEL_OS=linux
       script: tools/travis/build_bazel.sh
     - os: linux
-      dist: trusty
-      sudo: false
       env: CMAKE_OS=linux
       script: tools/travis/build_cmake.sh
     - os: osx

opencensus/trace/internal/grpc_trace_bin_fuzzer.cc

@@ -18,8 +18,8 @@
 
 using ::opencensus::trace::SpanContext;
 using ::opencensus::trace::propagation::FromGrpcTraceBinHeader;
-using ::opencensus::trace::propagation::ToGrpcTraceBinHeader;
 using ::opencensus::trace::propagation::kGrpcTraceBinHeaderLen;
+using ::opencensus::trace::propagation::ToGrpcTraceBinHeader;
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   absl::string_view header(reinterpret_cast<const char *>(Data), Size);

tools/format.sh

@@ -59,6 +59,9 @@ fi
 if [[ "$tools_check" == "y" ]]; then
   # For easier debugging: print the version because it affects the formatting.
   CMD=clang-format
+  if which clang-format-7 >/dev/null; then
+    CMD=clang-format-7
+  fi
   $CMD -version
   $CMD -i -style=Google \
     $($FIND -name '*.cc' -print -o -name '*.h' -print)

tools/travis/check_format.sh

@@ -15,11 +15,9 @@
 set -e
 set -x
 
-# Install buildifier if it's not present. It needs at least go 1.8.
-if ! which buildifier >/dev/null; then
-  eval "$(gimme 1.11)"
-  go get -v github.com/bazelbuild/buildtools/buildifier
-fi
+# Install buildifier.
+wget -O $HOME/bin/buildifier https://github.com/bazelbuild/buildtools/releases/download/2.2.1/buildifier
+chmod +x $HOME/bin/buildifier
 # Install cmake-format.
 pip install --user 'cmake_format>=0.5.2'
 # Check format.