Simplify include dependencies.

src/hydrogen.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 14 matching lines @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_HYDROGEN_H_
 #define V8_HYDROGEN_H_
 
 #include "v8.h"
 
 #include "ast.h"
 #include "compiler.h"
-#include "data-flow.h"
 #include "hydrogen-instructions.h"
 #include "zone.h"
 
 namespace v8 {
 namespace internal {
 
 // Forward declarations.
+class BitVector;
 class HEnvironment;
 class HGraph;
 class HLoopInformation;
 class HTracer;
 class LAllocator;
 class LChunk;
 class LiveRange;
 
 
 class HBasicBlock: public ZoneObject {
@@ skipping 1102 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_