[turbofan] Move GetCommonDominator to BasicBlock.

src/compiler/schedule.h

Index: src/compiler/schedule.h
diff --git a/src/compiler/schedule.h b/src/compiler/schedule.h
index ffce49fddd8624f0d162162c52604ba99fd4db53..e486289f5f383d457a87c9248921dc20fa294365 100644
--- a/src/compiler/schedule.h
+++ b/src/compiler/schedule.h
@@ -165,6 +165,10 @@ class BasicBlock FINAL : public ZoneObject {
   inline bool IsLoopHeader() const { return loop_end_ != NULL; }
   bool LoopContains(BasicBlock* block) const;
 
+  // Computes the immediate common dominator of {b1} and {b2}. The worst time
+  // complexity is O(N) where N is the height of the dominator tree.
+  static BasicBlock* GetCommonDominator(BasicBlock* b1, BasicBlock* b2);
+
  private:
   int32_t loop_number_;      // loop number of the block.
   int32_t rpo_number_;       // special RPO number of the block.