DevTools: [CanvasProfiler] Include a list of enabled WebGL extensions into the state obtained by CanvasAgent.getResourceState.

A list of enabled WebGL extensions can not be obtained directly via the WebGL API, but we can track this information.
Drive-by: provide some extension-related state if a corresponding extension is enabled.

BUG=253854
R=pfeldman,caseq@chromium.org

Review URL: https://chromiumcodereview.appspot.com/22950011

git-svn-id: svn://svn.chromium.org/blink/trunk@156103 bbb929c8-8fbe-4397-9dbb-9b2b20218538