Fix clip bounds of deferred filters with impl-side painting.

Blurs (and other pixel-moving filters, such as morphology and drop-shadow)
need to enlarge the filtered bounds to accomodate for their filter margins.
Skia's saveLayer() will do this automatically by inspecting the filters in
the SkPaint, but needs the kClipToLayer_SaveFlag to do so. Since this may
adjust the clip, we also add kClip_SaveFlag to restore it when done.

Covered by svg/filters/* when run with --enable-deferred-filters.

BUG=337831
R=fmalita@chromium.org

Review URL: https://codereview.chromium.org/164313003

git-svn-id: svn://svn.chromium.org/blink/trunk@167478 bbb929c8-8fbe-4397-9dbb-9b2b20218538
WebGL: Remove some unused members in WebGLRenderingContext.

In addition, mark TypedExtensionTracker's destructor virtual for clarity.

BUG=344393

Review URL: https://codereview.chromium.org/167893008

git-svn-id: svn://svn.chromium.org/blink/trunk@167479 bbb929c8-8fbe-4397-9dbb-9b2b20218538