Bug 1732464 - Reverse the order of calls to FindLineContaining in IsLocalAccAtLineStart, so that we can pass prevLineNum as a starting index to accelerate the second call. r=Jamie

Depends on D126587

Differential Revision: https://phabricator.services.mozilla.com/D126588

accessible/base/TextLeafRange.cpp

@@ -155,14 +155,14 @@ static bool IsLocalAccAtLineStart(LocalAccessible* aAcc) {
     // same line, so we're at the start.
     return true;
   }
-  nsAutoLineIterator it = thisBlock->GetLineIterator();
+  nsAutoLineIterator it = prevBlock->GetLineIterator();
   MOZ_ASSERT(it, "GetLineIterator impl in line-container blocks is infallible");
-  int32_t thisLineNum = it->FindLineContaining(thisLineFrame);
-  if (thisLineNum < 0) {
+  int32_t prevLineNum = it->FindLineContaining(prevLineFrame);
+  if (prevLineNum < 0) {
     // Error; play it safe.
     return true;
   }
-  int32_t prevLineNum = it->FindLineContaining(prevLineFrame);
+  int32_t thisLineNum = it->FindLineContaining(thisLineFrame, prevLineNum);
   // if the blocks and line numbers are different, that means there's nothing
   // before us on the same line, so we're at the start.
   return thisLineNum != prevLineNum;