Replace incorrectly used STACK_ALLOCATED with DISALLOW_NEW

TestVector is used inside WTF::Vector, hence isn't stack allocated.

Co-incidentally, we've discovered it during go/miracleptr project when
converted raw pointers to CheckedPtr wrapper, which have non-trivial
default constructor & destructor (when using the BackupRefPtr variant),
thus requiring placement |new|.

Bug: 1080832
Change-Id: Ia5e8b410e4cf8609783c8a3ee78d6c3d115513b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2448712
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813621}

third_party/blink/renderer/platform/audio/vector_math_test.cc

@@ -70,7 +70,7 @@ bool Equal(float a, float b) {
 // blink::vector_math functions.
 template <typename T>
 class TestVector {
-  STACK_ALLOCATED();
+  DISALLOW_NEW();
 
   class Iterator {
     STACK_ALLOCATED();