Add .clang-format and run clang-format on runtime/platform.

runtime/platform/text_buffer.cc

Index: runtime/platform/text_buffer.cc
diff --git a/runtime/platform/text_buffer.cc b/runtime/platform/text_buffer.cc
index b06c49fd80b7d4c2f63301ee79fe791a9c5214c6..b44ed6941f06a7b0a2d16acfab7d2c0009fb4e82 100644
--- a/runtime/platform/text_buffer.cc
+++ b/runtime/platform/text_buffer.cc
@@ -52,8 +52,7 @@ void TextBuffer::AddChar(char ch) {
 }
 
 
-void TextBuffer::AddRaw(const uint8_t* buffer,
-                        intptr_t buffer_length) {
+void TextBuffer::AddRaw(const uint8_t* buffer, intptr_t buffer_length) {
   EnsureCapacity(buffer_length);
   memmove(&buf_[msg_len_], buffer, buffer_length);
   msg_len_ += buffer_length;