[NaCl SDK] Make is easier to override linux host compiler

Switch from HOST_CC/HOST_CC/etc to the more standard
CC/CXX/etc for the names of the varaibles in the
SDK example build system.

This allow things like "CXX=clang++ make TOOLCHAIN=linux".

Also, fix kernel_wrap.h so that it compiles with
clang++ on desktop linux.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/85813004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237472 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237472
Remove JsonPrefStore pruning of empty values on write.

Written from https://codereview.chromium.org/12092021

The entire source code was surveyed for existing list/dict prefs for which this change could be problematic, it doesn't look like anything is relying on this internal detail of the API, see this for details: https://docs.google.com/a/chromium.org/spreadsheet/ccc?key=0AtwXJ4IPPZBAdG9rX3RTc3k5Z1pyN3U4b3d4Tkota3c#gid=0

TBR=joth (for minor android_webview side-effects)
BUG=323346

Review URL: https://codereview.chromium.org/81183005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237473 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237473