[Interpreter] Fix cctest/test-bytecode-generator/IfConditions.

Avoid hard-coding expected parameter indices.  These depend on the
frame size which can vary (e.g. if embedded constant pools are
enabled).

R=oth@chromium.org, rmcilroy@chromium.org, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1375373002

Cr-Commit-Position: refs/heads/master@{#31049}

test/cctest/interpreter/test-bytecode-generator.cc

@@ -789,7 +789,7 @@ TEST(IfConditions) {
        kPointerSize,
        2,
        19,
-       {B(Ldar), R(-5),                //
+       {B(Ldar), R(helper.kLastParamIndex),  //
         B(Star), R(0),                       //
         B(LdaZero),                          //
         B(TestLessThanOrEqual), R(0),        //
@@ -809,9 +809,9 @@ TEST(IfConditions) {
        kPointerSize,
        3,
        17,
-       {B(Ldar), R(-6),         //
+       {B(Ldar), R(helper.kLastParamIndex - 1),  //
         B(Star), R(0),                           //
-        B(Ldar), R(-5),         //
+        B(Ldar), R(helper.kLastParamIndex),      //
         B(TestIn), R(0),                         //
         B(JumpIfFalse), U8(7),                   //
         B(LdaConstant), U8(0),                   //
@@ -872,9 +872,9 @@ TEST(IfConditions) {
        122,
        {
 #define IF_CONDITION_RETURN(condition)    \
-  B(Ldar), R(-6),                      \
+  B(Ldar), R(helper.kLastParamIndex - 1), \
   B(Star), R(0),                          \
-  B(Ldar), R(-5),                      \
+  B(Ldar), R(helper.kLastParamIndex),     \
   B(condition), R(0),                     \
   B(JumpIfFalse), U8(7),                  \
   B(LdaSmi8), U8(1),                      \