RFR: 8270479: WebKit 612.1 build fails with Visual Studio 2017

[Kevin Rushforth]

On Wed, 14 Jul 2021 23:30:54 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> This fix allows the latest WebKit 612.1 to compile with Visual Studio 2017. For the jfx mainline, our current toolchain for Windows is VS2019 16.9.3, but we would like to continue to allow developers to build with VS 2017.
> 
> The JavaFX 11 code line still uses VS2017 (15.9.24), so we must fix this in the `jfx11u` code line in any case. Fixing it mainline first and then backporting it will allow the native WebKit code to remain in sync between mainline and jfx11u as well as keeping JavaFX buildable on VS2017 for a while longer.
> 
> As noted in the JBS bug report, eventually we will need to upgrade all code lines to a minimum of VS2019 for building WebKit, but this fix allows us to delay that for a while longer.
> 
> ## Notes to Reviewers
> 
> There were two problems that needed to be fixed:
> 
> *  `WebCore/inspector/InspectorOverlay.cpp` fails to compile with an error that "conversion from 'const int' to 'float' requires a narrowing conversion". The fix is to initialize the two `constexpr` variables with float constants instead of integer constants.
> * `jfxwebkit.dll` fails to link with 4 duplicate symbols due to VS2017's incomplete (or buggy) support for inline constant variables. The fix is to move the definition of those 4 constant variables from `Node.h` to `Node.cpp` and define them as runtime constants. 
> 
> I qualified both changes with `#if PLATFORM(JAVA)` so our local modifications are clearly identified. I could have further qualified the second of these two changes (there's no point in doing it for the first) with `&& OS(WINDOWS)` but chose to be consistent on all OS platforms.

@johanvos @tiainen Can one of you be the second reviewer?

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PR: https://git.openjdk.java.net/jfx/pull/576