Added bounds checking to GetNameFromTT to handle corrupt files.

Added bounds checking to GetNameFromTT to handle corrupt files.
This patch adds bounds checking to the names buffer passed to GetNameFromTT.
There are observed crashes in this function where data is read outside of the
bounds allocated and passed to GetNameFromTT. There's no reason that this
function should ever try and read outside of the allocated bounds.

BUG=583037

[forshaw, 2016-03-24 13:32:46]

forshaw@chromium.org changed reviewers:
+ tsepez@chromium.org

[forshaw, 2016-03-24 13:32:47]

Tom, Could you PTAL at this patch. It's another problem which we've encountered
with win32k lockdown due presumably to corrupt font files of some sort. It could
in theory affect other platforms such as Mac which share the same code.

[Tom Sepez, 2016-03-24 16:07:06]

Your stuff is fine, just a bunch of pre-existing nits we should fix while we're
in here.  LGTM after addressing nits.

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
File core/fxge/ge/fx_ge_fontmap.cpp (right):

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
core/fxge/ge/fx_ge_fontmap.cpp:699: const uint8_t* ptr = name_table;
nit: Do we need this local?  Can we just use (and later increment) name_table
instead?

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
core/fxge/ge/fx_ge_fontmap.cpp:710: ptr += 6;
nit: here we'd just increment name_table if we got rid of the local.

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
core/fxge/ge/fx_ge_fontmap.cpp:716: for (int i = 0; i < name_count; i++) {
nit: |i| probably should be a FX_DWORD to avoid signed/unsigned comparisons.

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
core/fxge/ge/fx_ge_fontmap.cpp:722: ptr += 12;
nit: maybe line 716 says "for (...; i++, ptr += 12) {" instead of doing this
here so that the two stay lock-step if someday someone wants to stick a
"continue" in this loop for some reason ...

https://codereview.chromium.org/1829013002/diff/20001/core/fxge/ge/fx_ge_font...
core/fxge/ge/fx_ge_fontmap.cpp:739: return (bytes_read == size) ?
GetNameFromTT(buffer_ptr, bytes_read, 6)
nit: () not needed.

[Tom Sepez, 2016-03-24 17:37:58]

Moved to https://codereview.chromium.org/1830243003/ for landing.