Implement Double.{toString, toStringAsExponential, toStringAsPrecision}

tests/language/language.status

Index: tests/language/language.status
diff --git a/tests/language/language.status b/tests/language/language.status
index 31c24d409d05aae8f56826a2fb4823f5cc033ebf..b0ad5846dcbf393234cd540115991c66191c72ca 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -113,6 +113,7 @@ Constructor4Test: Fail       # Issue 286
 Constructor5Test: Fail       # Issue 8440015 + 'super' initializer does not parse
 Constructor6Test: Fail       # Issue 8440015 + 'super' initializer does not parse
 DefaultFactoryLibraryTest: Fail          # Issue 514
+DoubleToString: Fail         # Prints "3" instead of "3.0" (since it doesn't distinguish ints and doubles).
 DivByZeroTest: Fail          # Bug 5184183
 DynamicTest: Fail            # Bug 5527899.
 ExampleConstructorTest: Fail # Bug 4205742.
@@ -199,7 +200,7 @@ TypedMessageTest: Fail # Bug 5246195
 
 
 [ $component == frog ]
-ToStringAsFixedTest: Fail # fails due to rounding in constant propagation
+DoubleToStringAsFixedTest: Fail # fails due to rounding in constant propagation and -0.0.
 
 [ $component == frogsh ||  $component == frog || ($component == webdriver && ($browser == chrome || $browser == ff || $browser == safari)) || $component == frogium ]
 Factory3Test: Fail # Issue 417
@@ -211,6 +212,7 @@ FactoryImplementationTest: Fail # Issue 523
 PseudoKWTest: Fail  # Issue 356
 NamingTest: Fail    # Issue 356
 DuplicateImplementsTest: Skip   # Issue 976
+DoubleToString: Fail     # Prints "3" instead of "3.0" (since it doesn't distinguish ints and doubles).
 
 SavannahTest: Skip # TODO(jimhug): Seems flaky on some configs - investigate.
 
@@ -340,13 +342,13 @@ ImplicitClosureTest: Fail
 MethodBindingTest: Fail
 Prefix15Test: Fail
 StringConcatTest: Fail
-ToStringAsFixedTest: Pass,Fail # Passes in 32-bit Safari, but fails in 64-bit Issue #1220
+DoubleToStringAsFixedTest: Pass,Fail # Passes in 32-bit Safari, but fails in 64-bit Issue #1220
 
 [ $component == webdriver && $browser == ff ]
 NamingTest: Fail
 StackOverflowTest: Fail
 StringConcatTest: Fail
-ToStringAsFixedTest: Fail
+DoubleToStringAsFixedTest: Fail
 
 [ $component == webdriver && $browser == ie && ($system == linux || $system == mac) ]
 *: Skip