MediaElementAudioSourceNode::dispose() should call HTMLMediaElement::setAudioSourceNode(0) in oilpan builds

Currently HTMLMediaElement::setAudioSourceNode(0) is called only in non-oilpan builds.
However, there is no reason why oilpan builds cannot call HTMLMediaElement::setAudioSourceNode(0).
It's better to call it both in oilpan builds and non-oilpan builds and reduce #if branches.

BUG=340522

Review URL: https://codereview.chromium.org/456273002

git-svn-id: svn://svn.chromium.org/blink/trunk@179939 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rebaseline svg/custom/pending-resource-after-removal.xhtml

Auto-rebaseline r179870 for r179857 appears to have failed with respect to Mac10.8.

TBR=wangxianzhu@chromium.org
BUG=

Review URL: https://codereview.chromium.org/461583002

git-svn-id: svn://svn.chromium.org/blink/trunk@179940 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add an ASSERT to verify that AudioNode::dispose() is always called

AudioNode::dispose() must be called before the AudioNode is destructed.
This is currently guaranteed in both oilpan builds and non-oilpan builds.
However the logic is not trivial, so this CL adds the ASSERT about it.

BUG=340522

Review URL: https://codereview.chromium.org/455353002

git-svn-id: svn://svn.chromium.org/blink/trunk@179941 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Cleanup namespace usage in public/platform/{Platform,Web[A-M]*}.h.

- Merge multiple |namespace blink {}| blocks
- Remove unnecessary blink:: prefixes
- Make blank lines consistent

BUG=

Review URL: https://codereview.chromium.org/457353002

git-svn-id: svn://svn.chromium.org/blink/trunk@179942 bbb929c8-8fbe-4397-9dbb-9b2b20218538