Merge all Hydrogen phase declarations into hydrogen-phases.h.

src/hydrogen-dce.cc

Index: src/hydrogen-dce.cc
diff --git a/src/hydrogen-dce.cc b/src/hydrogen-dce.cc
index 4ad32d2e4c8968d03781e5bf67e618ef6b14fb2d..5762687b0c90fa56cbe40ffc3a1a63b4bbe72de5 100644
--- a/src/hydrogen-dce.cc
+++ b/src/hydrogen-dce.cc
@@ -25,8 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include "hydrogen-dce.h"
-#include "v8.h"
+#include "hydrogen-phases.h"
 
 namespace v8 {
 namespace internal {