Reduces the number of callers of the synchronous IPC in TextInputClientMac::GetAttributedSubstringFromRange() (so that eventually we can remove it). Note: This is the second attempt to commit cl https://codereview.chromium.org/1313553006, which caused regression crbug.com/528929, because the point getten from selection range may not be accurate to get the string through GetStringAtPoint. This cl fixes that issue by leveraging TextInputClientMsg_StringForRange IPCs instead of TextInputClientMsg_StringAtPoint. The change is cross browser & blink so it is 2-way patches. This cl is based on the blink cl https://codereview.chromium.org/1329103002. TextInputClientObserver::OnStringForRange() will send the IPC TextInputClientReplyMsg_GotStringForRange to carry the basepiont info, which is got by the new change in blink. So this cl should be landed after https://codereview.chromium.org/1329103002 is landed. TBR=sievers@chromium.org BUG=121917 TEST=crbug.com/528929 not repro; Select multiple words and lookup dictionary by context menu can work well; Select non-English words (e.g. Japanese/Chinese) and lookup dictionary by context menu can work well. Review URL: https://codereview.chromium.org/1318483007 Cr-Commit-Position: refs/heads/master@{#350164}