Move DateMath weekdayName/monthName arrays to .rodata section

Move WTF::DateMath's weekdayName/monthName arrays from
.data.rel.ro.local section to .rodata section by leveraging the
fact that all the strings held in these arrays have the same size.
We can therefore define the arrays as:
const char weekdayName[7][4] = { ... };
instead of
const char* const weekdayName[7] = { ... };

This gets rid of all pointers and enables placing these arrays in
readonly memory.

This makes sure that they are shared between different library
instances, and should help saving RAM on mobile. This also reduces
the number of relocations in libchromeview_prebuilt.so by 31
according to relinfo.

BUG=249746

Review URL: https://codereview.chromium.org/29293002

git-svn-id: svn://svn.chromium.org/blink/trunk@159981 bbb929c8-8fbe-4397-9dbb-9b2b20218538