PPC: Fix "Remove inlined marking part."

Revert mistaken removal of JumpIfBlack prototype.

R=hpayer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=chromium:561449
LOG=n

Review URL: https://codereview.chromium.org/1544043002

Cr-Commit-Position: refs/heads/master@{#33030}

src/ppc/macro-assembler-ppc.h

@@ -212,6 +212,9 @@ class MacroAssembler : public Assembler {
   void HasColor(Register object, Register scratch0, Register scratch1,
                 Label* has_color, int first_bit, int second_bit);
 
+  void JumpIfBlack(Register object, Register scratch0, Register scratch1,
+                   Label* on_black);
+
   // Checks the color of an object.  If the object is white we jump to the
   // incremental marker.
   void JumpIfWhite(Register value, Register scratch1, Register scratch2,