Revert 157198 "Possible fix for a Mac performance regression."

> Possible fix for a Mac performance regression.
> 
> Introduced in
> http://src.chromium.org/viewvc/blink/trunk/Source/wtf/Vector.h?revision=157005
> 
> We now do the minimal amount of work possible on Vector destruction. We should
> now be faster than ever before:
> - The most common case is actually a totally unused Vector with no inline
> storage. In this case, we can bail and do no other work, if the buffer pointer
> is NULL.
> - There's no need to set m_size to 0 in the destructor; we've already checked
> that it is 0 and if not called resize(0) which will set it to 0.
> - In the Vector with inline storage case, we once again check m_size before
> calling shrink(), which might not be inline. It is common for m_size to be 0.
> 
> This also saves >50KB on a GCC Release build. clang, as usual, is barely
> affected on account of its less aggressive inlining.
> 
> 
> BUG=283760
> 
> Review URL: https://chromiumcodereview.appspot.com/23455034

TBR=cevans@chromium.org

Review URL: https://codereview.chromium.org/23475023

git-svn-id: svn://svn.chromium.org/blink/trunk@157266 bbb929c8-8fbe-4397-9dbb-9b2b20218538