return NULL if we failed to allocate a cairo surface, rather than waiting for skia to

return NULL if we failed to allocate a cairo surface, rather than waiting for skia to
crash with a null-bitmap-ptr. The callers already check for a NULL-BitmapPlatformDevice
return value.

Places where we perform this check/return on other platforms

bitmap_platform_device_win.cc#187 iff CreateDIBSection failed
bitmap_platform_device_mac.cc#120,144
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=148959

[reed1, 2012-07-30 15:25:14]

control #19 https://chromiumcodereview.appspot.com/10533136

[vandebo (ex-Chrome), 2012-07-30 16:13:01]

LGTM