Constant fold math and string operations.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 9e3c397229c2f871c79a7d9306033d6dd2120868..0b12375599cd09084d29751084ac3457f44452b7 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -968,6 +968,7 @@ 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);