Get rid of the tryFast*alloc API.

Also removes WTF_MALLOC_VALIDATION, which we do not use and therefore the complexity it adds is unwelcome.

There are various benefits:
1) The standard ones from having less code and less complexity.
2) The API doesn't actually work, so every new caller becomes a possible bug. On (at least) Linux and Windows, our underlying malloc is tcmalloc which is hard-wired to crash on allocation failure. So tryFast*alloc can never return a fail for most of our users.
3) We've removed an inconsistency between platforms: I think tryFast*alloc might actually work as advertised on Mac, because of the built-in copy of tcmalloc.

This also removes 500KB of guff from the Linux x64 chrome debug binary. A negligible effect on the release binary, sadly. 


BUG=none
TEST=compile, webkit_tests pass

Review URL: https://chromiumcodereview.appspot.com/22038002

git-svn-id: svn://svn.chromium.org/blink/trunk@155495 bbb929c8-8fbe-4397-9dbb-9b2b20218538