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

.clang-format

Index: .clang-format
diff --git a/.clang-format b/.clang-format
new file mode 100644
index 0000000000000000000000000000000000000000..96325aea2888143f4941894c782d9dbebd9833ed
--- /dev/null
+++ b/.clang-format
@@ -0,0 +1,16 @@
+# Defines the Chromium style for automatic reformatting.
+# http://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: Chromium
+
+# Keep up to 2 blank lines. More blank lines are removed.
+MaxEmptyLinesToKeep: 2
+
+# clang-format doesn't seem to do a good job of this for longer comments.
+ReflowComments: 'false'
+
+# We have lots of these. Though we need to put them all in curly braces,
+# clang-format can't do that.
+AllowShortIfStatementsOnASingleLine: 'true'
+
+# Put escaped newlines into the rightmost column.
+AlignEscapedNewlinesLeft: false