Add assembly constraints to disable some overly aggressive GCC optimizations

GCC's optimizer is getting more aggressive. It is no longer good
enough to just pass the address of a structure as an input parameter
to assembly code. The assembly code must also mark "memory" as getting
clobbered, even if it only wants to read from the structure. This
seems to be a result of strict aliasing and the lack of an ability for
the assembly code to clearly say which pointers it dereferences.

Furthermore, if the assembly code touches the stack (e.g. uses
"push"), it must now mark the stack pointer as getting
clobbered. Otherwise, GCC assumes that the red zone won't be
clobbered, and that it is possible to use the stack pointer as an
input register.

BUG=none
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=29829

[agl, 2009-10-22 21:44:31]

LGTM