There should only be one way to get the system memory size.

There should only be one way to get the system memory size.
<https://webkit.org/b/144081>

Reviewed by Antti Koivisto.

Source/WebKit/mac:

* Misc/WebKitSystemBits.h:
* Misc/WebKitSystemBits.m:
(WebMemorySize): Deleted.
* WebView/WebView.mm:
(+[WebView _setCacheModel:]):
(roundUpToPowerOf2): Deleted.

Source/WebKit/win:

* WebView.cpp:
(WebView::setCacheModel):

Source/WebKit2:

* NetworkProcess/cocoa/NetworkProcessCocoa.mm:
(WebKit::NetworkProcess::platformSetCacheModel):
(WebKit::memorySize): Deleted.
* WebProcess/cocoa/WebProcessCocoa.mm:
(WebKit::WebProcess::platformSetCacheModel):
(WebKit::memorySize): Deleted.

Source/WTF:

Merge all the logic from other RAM size fetcher helpers into WTF's.

Darwin ports now use host_info() instead of sysctl(), since that was the more common way
of doing this.

Also bumped the fallback answer from 128 MB to 512 MB to bring it closer to today's hardware.

Finally, the number is rounded up to the next multiple of 128 MB, to avoid misunderstandings
on some systems where the number returned by the kernel is slightly lower than the marketing
number. Removed the "fudging" that was used in some places, since this fixes that cleanly.

* wtf/RAMSize.cpp:
(WTF::computeRAMSize):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@183181 268f45cc-cd09-0410-ab3c-d52691b4dbfc