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

runtime/platform/hashmap.h

Index: runtime/platform/hashmap.h
diff --git a/runtime/platform/hashmap.h b/runtime/platform/hashmap.h
index 1cd8a4a2331da44dfa5cd4ee233e5b499cfee24e..1fd1235153dda9e5e3b02ad6685dd311a689cc92 100644
--- a/runtime/platform/hashmap.h
+++ b/runtime/platform/hashmap.h
@@ -11,9 +11,9 @@ namespace dart {
 
 class HashMap {
  public:
-  typedef bool (*MatchFun) (void* key1, void* key2);
+  typedef bool (*MatchFun)(void* key1, void* key2);
 
-  typedef void (*ClearFun) (void* value);
+  typedef void (*ClearFun)(void* value);
 
   // initial_capacity is the size of the initial hash map;
   // it must be a power of 2 (and thus must not be 0).
@@ -21,9 +21,7 @@ class HashMap {
 
   ~HashMap();
 
-  static bool SamePointerValue(void* key1, void* key2) {
-    return key1 == key2;
-  }
+  static bool SamePointerValue(void* key1, void* key2) { return key1 == key2; }
 
   static uint32_t StringHash(char* key) {
     uint32_t hash_ = 0;