On Linux the generated ninja files use path/libbase.a as target name.
In the Mac ninja file the target is just libbase.a.
As we have two libbase.a (base/base.gyp and media/base/media_base.gyp) the linking stage fails to include both libs.
Solve by renaming media_base.gyp's base target to media_base
For WebM contents, it is possible that we may receive some NewSampleEvent
before receiving ParserInitEvent. This is because init event is fired
after analyzing a video block which could come after an audio block.
Also modified Flush() function to return a bool to indicate whether the
the flush is successful and whether the samples are handled correctly.
And added macro to ensure Flush() and Parse() results are handled.
Fixes#71
Change-Id: I2294d6f529f54e4578344916559bb1bc116c745a