[Mac] Validate the selection range before using it for text suggestions.

It looks like Blink can report an invalid selection range back to the
browser. This change treats invalid ranges like the empty string for the
purpose of generating suggestions, and adds a DCHECK for this condition.

Bug: 893038
Change-Id: I2afa5065d7eeebb6cc61030277f86b488a69388b
Reviewed-on: https://chromium-review.googlesource.com/c/1351530
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612882}

content/browser/renderer_host/render_widget_host_view_mac.mm

@@ -11,6 +11,7 @@
 
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/debug/dump_without_crashing.h"
 #include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/mac/mac_util.h"
@@ -655,6 +656,24 @@ void RenderWidgetHostViewMac::OnTextSelectionChanged(
   const TextInputManager::TextSelection* selection = GetTextSelection();
   if (!selection)
     return;
+
+  if (!selection->range().IsValid()) {
+    LOG(ERROR) << "Invalid selection range.";
+    base::debug::DumpWithoutCrashing();
+    return;
+  }
+
+  gfx::Range text_range(selection->offset(),
+                        selection->text().length() + selection->offset());
+  if (selection->range().GetMin() < text_range.GetMin() ||
+      selection->range().GetMax() > text_range.GetMax()) {
+    LOG(ERROR) << "Selection with range " << selection->range().ToString()
+               << " in a chunk of text which only covers "
+               << text_range.ToString() << ".";
+    base::debug::DumpWithoutCrashing();
+    return;
+  }
+
   ns_view_bridge_->SetTextSelection(selection->text(), selection->offset(),
                                     selection->range());
 }

content/browser/renderer_host/render_widget_host_view_mac_unittest.mm

@@ -187,9 +187,10 @@ requestCandidatesForSelectedRange:(NSRange)selectedRange
   return sequenceNumber_;
 }
 
-- (void (^)(NSInteger sequenceNumber,
-            NSArray<NSTextCheckingResult*>* candidates))lastCompletionHandler {
-  return lastCompletionHandler_;
+- (base::mac::ScopedBlock<void (^)(NSInteger sequenceNumber,
+                                   NSArray<NSTextCheckingResult*>* candidates)>)
+    takeCompletionHandler {
+  return std::move(lastCompletionHandler_);
 }
 
 @end
@@ -2123,9 +2124,7 @@ TEST_F(InputMethodMacTest, TouchBarTextSuggestionsReplacement) {
     tab_view()->SelectionChanged(kOriginalString, 3, gfx::Range(3, 3));
 
     NSInteger firstSequenceNumber = [spellChecker sequenceNumber];
-    base::mac::ScopedBlock<void (^)(NSInteger sequenceNumber,
-                                    NSArray<NSTextCheckingResult*>* candidates)>
-        firstCompletionHandler([[spellChecker lastCompletionHandler] retain]);
+    auto firstCompletionHandler = [spellChecker takeCompletionHandler];
 
     EXPECT_NE(nil, (id)firstCompletionHandler.get());
     EXPECT_EQ(0U, candidate_list_item().candidates.count);
@@ -2143,7 +2142,7 @@ TEST_F(InputMethodMacTest, TouchBarTextSuggestionsReplacement) {
     EXPECT_EQ(0U, candidate_list_item().candidates.count);
 
     // But calling the current handler should work.
-    [spellChecker lastCompletionHandler](
+    [spellChecker takeCompletionHandler].get()(
         [spellChecker sequenceNumber],
         @[ static_cast<NSTextCheckingResult*>(fakeResult) ]);
     base::RunLoop().RunUntilIdle();
@@ -2178,6 +2177,11 @@ TEST_F(InputMethodMacTest, TouchBarTextSuggestionsInvalidSelection) {
     SetTextInputType(tab_view(), ui::TEXT_INPUT_TYPE_TEXT);
     candidate_list_item().allowsCollapsing = NO;
 
+    if (auto completionHandler = [spellChecker takeCompletionHandler]) {
+      completionHandler.get()([spellChecker sequenceNumber], @[]);
+      base::RunLoop().RunUntilIdle();
+    }
+
     FakeTextCheckingResult* fakeResult =
         [FakeTextCheckingResult resultWithRange:NSMakeRange(0, 3)
                               replacementString:@"foo"];
@@ -2187,10 +2191,12 @@ TEST_F(InputMethodMacTest, TouchBarTextSuggestionsInvalidSelection) {
     tab_view()->SelectionChanged(kOriginalString, 3,
                                  gfx::Range::InvalidRange());
 
-    [spellChecker lastCompletionHandler](
+    if (auto completionHandler = [spellChecker takeCompletionHandler]) {
+      completionHandler.get()(
           [spellChecker sequenceNumber],
           @[ static_cast<NSTextCheckingResult*>(fakeResult) ]);
       base::RunLoop().RunUntilIdle();
+    }
 
     EXPECT_NE(nil, candidate_list_item().candidates);
     EXPECT_EQ(0U, candidate_list_item().candidates.count);