Ensure that matches are not scrolled into after the findbar has been …

…closed (PR 10100 follow-up)

Despite all highlighted matches being removed in response to the 'findbarclose' event, there's a risk that a match could still be scrolled into view *after* the findbar has been closed[1].
Hence we need to ensure that long running searches, particularily those happening in large and/or slow loading documents[2], are ignored as well.

---
[1] The match is hidden, as expected, but the document could still scroll unexpectedly.
[2] Large documents loaded with `disableAutoFetch = true` and `disableStream = true` set are particularily susceptible to this issue.

web/pdf_find_controller.js

@@ -112,10 +112,10 @@ class PDFFindController {
     this._updateUIState(FindState.PENDING);
 
     this._firstPageCapability.promise.then(() => {
+      // If the document was closed before searching began, or if the search
+      // operation was relevant for a previously opened document, do nothing.
       if (!this._pdfDocument ||
           (pdfDocument && this._pdfDocument !== pdfDocument)) {
-        // If the document was closed before searching began, or if the search
-        // operation was relevant for a previously opened document, do nothing.
         return;
       }
       this._extractText();
@@ -150,6 +150,7 @@ class PDFFindController {
     this._offset = { // Where the find algorithm currently is in the document.
       pageIdx: null,
       matchIdx: null,
+      wrapped: false,
     };
     this._extractTextPromises = [];
     this._pageContents = []; // Stores the text for each page.
@@ -409,6 +410,7 @@ class PDFFindController {
       this._selected.pageIdx = this._selected.matchIdx = -1;
       this._offset.pageIdx = currentPageIndex;
       this._offset.matchIdx = null;
+      this._offset.wrapped = false;
       this._resumePageIdx = null;
       this._pageMatches.length = 0;
       this._pageMatchesLength = null;
@@ -552,17 +554,27 @@ class PDFFindController {
     // matches (from the UI) is async too such that the 'updatetextlayermatches'
     // events will always be dispatched in the expected order.
     this._firstPageCapability.promise.then(() => {
+      // Only update the UI if the document is open, and is the current one.
       if (!this._pdfDocument ||
           (pdfDocument && this._pdfDocument !== pdfDocument)) {
-        // Only update the UI if the document is open, and is the current one.
         return;
       }
+      // Ensure that a pending, not yet started, search operation is aborted.
       if (this._findTimeout) {
         clearTimeout(this._findTimeout);
         this._findTimeout = null;
-        // Avoid the UI being in a pending state if the findbar is re-opened.
-        this._updateUIState(FindState.FOUND);
       }
+      // Abort any long running searches, to avoid a match being scrolled into
+      // view *after* the findbar has been closed. In this case `this._offset`
+      // will most likely differ from `this._selected`, hence we'll also ensure
+      // that any new search operation will always start with a clean slate.
+      if (this._resumePageIdx) {
+        this._resumePageIdx = null;
+        this._dirtyMatch = true;
+      }
+      // Avoid the UI being in a pending state when the findbar is re-opened.
+      this._updateUIState(FindState.FOUND);
+
       this._highlightMatches = false;
       this._updateAllPages(); // Wipe out any previously highlighted matches.
     });