[a11y] Update DCHECK on GetTextContainerForPlainTextField()

This CL updates DCHECK for checking the child count of the text
field on GetTextContainerForPlainTextField(). The text field
could have a sibling of the static text when it has a
placeholder break element. So, this change increases the child
count.

AX-Relnotes: n/a

Bug: 1137292
Change-Id: Ib6d6826ce23156e8d5562d9561ad8061d46b6946
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2578718
Commit-Queue: Julie Kim <jkim@igalia.com>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836355}

content/browser/accessibility/accessibility_auralinux_browsertest.cc

@@ -2157,4 +2157,20 @@ IN_PROC_BROWSER_TEST_F(AccessibilityAuraLinuxBrowserTest,
   }
 }
 
+// Tests if it does not DCHECK when textarea has a placeholder break element.
+IN_PROC_BROWSER_TEST_F(AccessibilityAuraLinuxBrowserTest,
+                       TestGetTextContainerFromTextArea) {
+  std::string content = std::string("<textarea style=\"height:100px;\">hello") +
+                        std::string("\n") + std::string("</textarea>");
+  LoadInitialAccessibilityTreeFromHtml(content);
+
+  AtkText* atk_text = FindNode(ATK_ROLE_ENTRY);
+  AtkTextRectangle atk_rect;
+  // atk_text_get_range_extents() calls GetTextContainerForPlainTextField() and
+  // DCHECK on checking children counts.
+  atk_text_get_range_extents(atk_text, 0, 7, AtkCoordType::ATK_XY_SCREEN,
+                             &atk_rect);
+  g_object_unref(atk_text);
+}
+
 }  // namespace content

content/browser/accessibility/browser_accessibility.cc

@@ -64,10 +64,12 @@ const BrowserAccessibility* GetTextContainerForPlainTextField(
   // ---- Generic container  (optional, only occurs in some controls)
   // ------ Static text   <-- (optional, does not exist if field is empty)
   // -------- Inline text box children (can be multiple)
+  // ------ Line Break (optional,  a placeholder break element if the text data
+  //                    ends with '\n' or '\r')
   // This method will return the lowest generic container.
   const BrowserAccessibility* child = text_field.InternalGetFirstChild();
   DCHECK_EQ(child->GetRole(), ax::mojom::Role::kGenericContainer);
-  DCHECK_LE(child->InternalChildCount(), 1u);
+  DCHECK_LE(child->InternalChildCount(), 2u);
   if (child->InternalChildCount() == 1) {
     const BrowserAccessibility* grand_child = child->InternalGetFirstChild();
     if (grand_child->GetRole() == ax::mojom::Role::kGenericContainer) {