Chandler's PI, Marlowe, has received a call from a woman whose voice he doesn't recognize. She tells him to see a lawyer named Rush Madder, and it's Madder whom Marlowe is talking to here. Marlowe is sure that Madder had the woman call, but when he asks Madder who she is, Madder asks, "Did somebody phone you?"
Marlowe makes the "count clouds" comment and threatens to go to the police. Madder stops him and admits that the caller was friend of his.
So Marlowe was sure that Madder was lying to him, and his comment likely means stop wasting my time by feigning ignorance. Counting clouds is as pointless and useless occupation and as big a waste of time as Madder's lying and stalling.