[ia32] Add disassembler support for 'pause'

R=mstarzinger@chromium.org

Bug: chromium:849656
Change-Id: I34effca4770f732216b93b5e4e8c28383f2f9963
Reviewed-on: https://chromium-review.googlesource.com/1087271Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53534}

src/ia32/disasm-ia32.cc

@@ -2516,6 +2516,9 @@ int DisassemblerIA32::InstructionDecode(v8::internal::Vector<char> out_buffer,
         } else if (*(data+1) == 0xAB) {
           data += 2;
           AppendToBuffer("rep_stos");
+        } else if (*(data + 1) == 0x90) {
+          data += 2;
+          AppendToBuffer("pause");
         } else {
           UnimplementedInstruction();
         }

test/cctest/test-disasm-ia32.cc

@@ -883,6 +883,7 @@ TEST(DisasmIa320) {
     __ Nop(i);
   }
 
+  __ pause();
   __ ret(0);
 
   CodeDesc desc;