attempt to multiply with overflow in texture_allocator on filter:blur with large radius

[mateon1]

This should be gracefully handled. Either use saturating multiplication, or detect the issue early.

This is caused by the same line as #18655, but with a different root cause.

<div style="filter: blur(999999px)">x</div>

attempt to multiply with overflow (thread RenderBackend, at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/texture_allocator.rs:55)
stack backtrace:
   0:     0x55d9d5820fb4 - backtrace::backtrace::libunwind::trace
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/backtrace/libunwind.rs:53
                         - backtrace::backtrace::trace<closure>
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/backtrace/mod.rs:42
   1:     0x55d9d581c9df - backtrace::capture::{{impl}}::new
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/capture.rs:64
   2:     0x55d9cfa363fe - servo::main::{{closure}}
                        at /shared/dev/rust/servo/ports/servo/main.rs:130
   3:     0x55d9d67ec2b6 - std::panicking::rust_panic_with_hook
                        at /checkout/src/libstd/panicking.rs:578
   4:     0x55d9d67ec0d4 - std::panicking::begin_panic<alloc::string::String>
                        at /checkout/src/libstd/panicking.rs:538
   5:     0x55d9d67ec049 - std::panicking::begin_panic_fmt
                        at /checkout/src/libstd/panicking.rs:522
   6:     0x55d9d67ebfda - std::panicking::rust_begin_panic
                        at /checkout/src/libstd/panicking.rs:498
   7:     0x55d9d6826410 - core::panicking::panic_fmt
                        at /checkout/src/libcore/panicking.rs:71
   8:     0x55d9d6826346 - core::panicking::panic
                        at /checkout/src/libcore/panicking.rs:51
   9:     0x55d9d3c10f33 - webrender::texture_allocator::{{impl}}::find_index_of_best_rect_in_bin
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/texture_allocator.rs:55
  10:     0x55d9d3c110a1 - webrender::texture_allocator::{{impl}}::find_index_of_best_rect
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/texture_allocator.rs:73
  11:     0x55d9d3c111b1 - webrender::texture_allocator::{{impl}}::allocate
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/texture_allocator.rs:86
  12:     0x55d9d3e96daf - webrender::tiling::{{impl}}::allocate
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/tiling.rs:912
  13:     0x55d9d3e97d05 - webrender::tiling::{{impl}}::allocate
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/tiling.rs:1056
  14:     0x55d9d3e979b9 - webrender::tiling::{{impl}}::allocate<webrender::tiling::ColorRenderTarget>
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/tiling.rs:1016
  15:     0x55d9d3e99a2c - webrender::tiling::{{impl}}::build
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/tiling.rs:1398
  16:     0x55d9d3be13a2 - webrender::frame_builder::{{impl}}::build
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/frame_builder.rs:2357
  17:     0x55d9d3e82a05 - webrender::frame::{{impl}}::build_frame::{{closure}}
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/frame.rs:1253
  18:     0x55d9d3da5e75 - core::option::{{impl}}::map<&mut webrender::frame_builder::FrameBuilder,webrender::tiling::Frame,closure>
                        at /checkout/src/libcore/option.rs:398
  19:     0x55d9d3e8270c - webrender::frame::{{impl}}::build_frame
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/frame.rs:1252
  20:     0x55d9d3e824f8 - webrender::frame::{{impl}}::build
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/frame.rs:1229
  21:     0x55d9d3e8f62a - webrender::render_backend::{{impl}}::render
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/render_backend.rs:106
  22:     0x55d9d3e91141 - webrender::render_backend::{{impl}}::process_document
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/render_backend.rs:400
  23:     0x55d9d3e91cf7 - webrender::render_backend::{{impl}}::run
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/render_backend.rs:468
  24:     0x55d9d3c1ea80 - webrender::renderer::{{impl}}::new::{{closure}}
                        at /shared/dev/rust/servo/.cargo/git/checkouts/webrender-c3596abe1cf4f320/0fd01ba/webrender/src/renderer.rs:1713
  25:     0x55d9d3b4bbaa - std::sys_common::backtrace::__rust_begin_short_backtrace<closure,()>
                        at /checkout/src/libstd/sys_common/backtrace.rs:136
  26:     0x55d9d3db0d53 - std::thread::{{impl}}::spawn::{{closure}}::{{closure}}<closure,()>
                        at /checkout/src/libstd/thread/mod.rs:400
  27:     0x55d9d3d757ea - std::panic::{{impl}}::call_once<(),closure>
                        at /checkout/src/libstd/panic.rs:296
  28:     0x55d9d3db24f2 - std::panicking::try::do_call<std::panic::AssertUnwindSafe<closure>,()>
                        at /checkout/src/libstd/panicking.rs:480
  29:     0x55d9d67f344c - panic_unwind::__rust_maybe_catch_panic
                        at /checkout/src/libpanic_unwind/lib.rs:99
  30:     0x55d9d3db10ec - std::panicking::try<(),std::panic::AssertUnwindSafe<closure>>
                        at /checkout/src/libstd/panicking.rs:459
  31:     0x55d9d3db0835 - std::panic::catch_unwind<std::panic::AssertUnwindSafe<closure>,()>
                        at /checkout/src/libstd/panic.rs:361
  32:     0x55d9d3b4eb8b - std::thread::{{impl}}::spawn::{{closure}}<closure,()>
                        at /checkout/src/libstd/thread/mod.rs:399
  33:     0x55d9d3b87aa3 - alloc::boxed::{{impl}}::call_box<(),closure>
                        at /checkout/src/liballoc/boxed.rs:728
  34:     0x55d9d67eaf3b - alloc::boxed::{{impl}}::call_once<(),()>
                        at /checkout/src/liballoc/boxed.rs:738
                         - std::sys_common::thread::start_thread
                        at /checkout/src/libstd/sys_common/thread.rs:24
                         - std::sys::imp::thread::{{impl}}::new::thread_start
                        at /checkout/src/libstd/sys/unix/thread.rs:90
  35:     0x7fdb32e2c493 - start_thread
  36:     0x7fdb32959abe - __clone
  37:                0x0 - <unknown>
ERROR:servo: attempt to multiply with overflow

[jdm]

cc @glennw

[glennw]

The code in question here no longer exists - the texture allocator was replaced with a deterministic slab-style allocator.