Add toDouble() helper, and use toFloat()/toDouble() for conversions

Source/bindings/core/v8/V8Binding.h

 /*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 * Copyright (C) 2012 Ericsson AB. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
@@ skipping 517 matching lines @@
 
 // Convert a value to a single precision float, which might fail.
 float toFloat(v8::Handle<v8::Value>, ExceptionState&);
 
 // Convert a value to a single precision float assuming the conversion cannot fail.
 inline float toFloat(v8::Local<v8::Value> value)
 {
     return static_cast<float>(value->NumberValue());
 }
 
+// Convert a value to a double precision float, which might fail.
+double toDouble(v8::Handle<v8::Value>, ExceptionState&);
+
 // Converts a value to a String, throwing if any code unit is outside 0-255.
 String toByteString(v8::Handle<v8::Value>, ExceptionState&);
 
 // Converts a value to a String, replacing unmatched UTF-16 surrogates with replacement characters.
 String toScalarValueString(v8::Handle<v8::Value>, ExceptionState&);
 
 inline v8::Handle<v8::Boolean> v8Boolean(bool value, v8::Isolate* isolate)
 {
     return value ? v8::True(isolate) : v8::False(isolate);
 }
@@ skipping 423 matching lines @@
 v8::Local<v8::Value> v8IteratorResult(v8::Isolate*, v8::Handle<v8::Value>);
 template <typename T>
 v8::Local<v8::Value> v8IteratorResult(ScriptState* scriptState, const T& value)
 {
     return v8IteratorResult(scriptState->isolate(), V8ValueTraits<T>::toV8Value(value, scriptState->context()->Global(), scriptState->isolate()));
 }
 
 } // namespace blink
 
 #endif // V8Binding_h