Update suppression for issue 49404 and 50630.

Update suppression for issue 49404 and 50630.

Merged those two issues in tracker as they seem to root from the same
cause.

In base::Base64Encode, we have these:
  std::string temp;
  temp.resize(...);
  ...
  modp_b64_encode(&(temp[0]...);

And Valgrind does not like use temp without initializing after resize.

BUG=49404
TEST=Valgrind memcheck should pass.

[xiyuan, 2010-08-02 17:20:53]

Tim's finding in crbug.com/49404 shows that the failure could be real instead of
false positive.

Closing this suppression update and investigate if a similar case could be found
for crbug.com/50630 where gfx::PNGCodec::EncodeBGRASkBitmap leaves some uninit
bytes in the buffer we passed to base::Base64Encode.