Constant fold math and string operations.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 890ef69dbbdb37d0473ffc903649bef24e688bba..772e1d7f66ec185212a9ec453598d81e329561e9 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -962,6 +962,7 @@ inline int NumberOfBitsSet(uint32_t x) {
 bool EvalComparison(Token::Value op, double op1, double op2);
 
 // Computes pow(x, y) with the special cases in the spec for Math.pow.
+double power_helper(double x, double y);
 double power_double_int(double x, int y);
 double power_double_double(double x, double y);