Setup valid pool pointer in assembler tests

runtime/vm/assembler_x64_test.cc

Index: runtime/vm/assembler_x64_test.cc
diff --git a/runtime/vm/assembler_x64_test.cc b/runtime/vm/assembler_x64_test.cc
index 00b845006d68910561c15d7e0afcb8b10e421761..38567f0cefe28065dea29e1ffd239ffc7f994893 100644
--- a/runtime/vm/assembler_x64_test.cc
+++ b/runtime/vm/assembler_x64_test.cc
@@ -1473,10 +1473,13 @@ ASSEMBLER_TEST_GENERATE(PackedDoubleNegate, assembler) {
     double a;
     double b;
   } constant0 = { 1.0, 2.0 };
+  __ pushq(PP);  // Save caller's pool pointer and load a new one here.
+  __ LoadPoolPointer(PP);
   __ movq(RAX, Immediate(reinterpret_cast<uword>(&constant0)));
   __ movups(XMM10, Address(RAX, 0));
   __ negatepd(XMM10);
   __ movaps(XMM0, XMM10);
+  __ popq(PP);  // Restore caller's pool pointer.
   __ ret();
 }
 
@@ -1493,10 +1496,13 @@ ASSEMBLER_TEST_GENERATE(PackedDoubleAbsolute, assembler) {
     double a;
     double b;
   } constant0 = { -1.0, 2.0 };
+  __ pushq(PP);  // Save caller's pool pointer and load a new one here.
+  __ LoadPoolPointer(PP);
   __ movq(RAX, Immediate(reinterpret_cast<uword>(&constant0)));
   __ movups(XMM10, Address(RAX, 0));
   __ abspd(XMM10);
   __ movaps(XMM0, XMM10);
+  __ popq(PP);  // Restore caller's pool pointer.
   __ ret();
 }