v8binding: Fix ToFloat to throw

Adds a missing check of exception_state.HadException().

Comment about crbug.com/939598 is not correct because of
    unrestricted float (Web IDL) => ToFloat (Blink)
    float (Web IDL) => ToRestrictedFloat (Blink)
In case of 'unrestricted float', it shouldn't throw an
exception.

Bug: 939598
Change-Id: Ibda1cb445b630f38a8e3ab52c6839a49020d6941
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574997Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652538}

third_party/blink/renderer/bindings/core/v8/v8_binding_for_core.h

@@ -372,9 +372,8 @@ inline float ToFloat(v8::Isolate* isolate,
                      v8::Local<v8::Value> value,
                      ExceptionState& exception_state) {
   double double_value = ToDouble(isolate, value, exception_state);
-  // TODO(crbug.com/939598): These cases should throw a TypeError instead
-  // of returning Infinity; but before fixing that, we must ensure that
-  // ToFloat is not called in cases where ToDouble should be called instead.
+  if (exception_state.HadException())
+    return 0;
   using Limits = std::numeric_limits<float>;
   if (UNLIKELY(double_value > Limits::max()))
     return Limits::infinity();