More aggressive DCHECKs for FrameTree::setName.

third_party/WebKit/Source/core/page/FrameTree.cpp

Index: third_party/WebKit/Source/core/page/FrameTree.cpp
diff --git a/third_party/WebKit/Source/core/page/FrameTree.cpp b/third_party/WebKit/Source/core/page/FrameTree.cpp
index 4b6e9d17b45d0d3ea6719c58cd470ee2c0147b38..5742191df101fb60dd771901f535fb76bb6c1d27 100644
--- a/third_party/WebKit/Source/core/page/FrameTree.cpp
+++ b/third_party/WebKit/Source/core/page/FrameTree.cpp
@@ -54,19 +54,22 @@ FrameTree::~FrameTree()
 
 void FrameTree::setName(const AtomicString& name)
 {
+    // This method should only be called for local frames
+    // (remote frames should be updated via setPrecalculatedName).
+    DCHECK(m_thisFrame->isLocalFrame());
+
+    // When this method is called, m_uniqueName should be already initialized.
+    // This assert helps ensure that early return (a few lines below) won't
+    // result in an uninitialized m_uniqueName.
+    DCHECK(!m_uniqueName.isNull()
+        || (m_uniqueName.isNull() && m_name.isNull() && !parent()));

[Łukasz Anforowicz, 2016/06/16 22:11:38]

I think it is important to move this DCHECK out of the "if" statement's body.

Before this CL, the DCHECK would fire in case where m_uniqueName is left in a
broken, uninitialized state.

After this CL, the DCHECK will fire in cases where m_uniqueName can
*potentially* be left in a broken, uninitialized state (because
FrameTree::setName was called at a bad time).

+
     // Do not recalculate m_uniqueName if there is no real change of m_name.
     // This is not just a performance optimization - other code relies on the
     // assumption that unique name shouldn't change if the assigned name didn't
     // change (i.e. code in content::FrameTreeNode::SetFrameName).
-    if (m_name == name) {
-        // Assert that returning early below won't leave m_uniqueName in an
-        // uninitialized state - it should only be null if m_name is also
-        // null and only if it is for the main frame.
-        // m_uniqueName.isNull() should imply m_name.isNull() && !parent().
-        // this FrameTree is for a main frame.
-        DCHECK(!m_uniqueName.isNull() || (m_name.isNull() && !parent()));
+    if (m_name == name)
         return;
-    }
 
     m_name = name;