[breakpad] DCHECK that crash key size is below limit.

Currently, Breakpad will silently truncate a crash key name with a
length above the limit of 40 characters. Unfortunately, trying to
retrieve the value of the key with crash_reporter::GetCrashKeyValue()
will fail, as the truncated name is not used for retrieval.

This CL adds a DCHECK for the crash key length, to avoid having
other people chasing the same problem as me when writing a test
for crash keys.

Change-Id: I6f08ddcb5df9589b7604f34fbeb2dbb6573b1b20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999220
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732520}

components/crash/core/common/crash_key.h

@@ -72,6 +72,7 @@ using CrashKeyString = crashpad::StringAnnotation<MaxLength>;
 
 namespace internal {
 
+constexpr size_t kCrashKeyStorageKeySize = 40;
 constexpr size_t kCrashKeyStorageNumEntries = 200;
 constexpr size_t kCrashKeyStorageValueSize = 128;
 

components/crash/core/common/crash_key_breakpad.cc

@@ -50,6 +50,10 @@ void ResetCrashKeyStorageForTesting() {
 }
 
 void CrashKeyStringImpl::Set(base::StringPiece value) {
+  // This check cannot be in the constructor because it is constexpr. Use _LT
+  // rather than _LE to account for the terminating \0.
+  DCHECK_LT(strlen(name_), kCrashKeyStorageKeySize);
+
   const size_t kValueMaxLength = index_array_count_ * kCrashKeyStorageValueSize;
 
   TransitionalCrashKeyStorage* storage = GetCrashKeyStorage();

components/crash/core/common/crash_key_internal.h

@@ -12,8 +12,10 @@
 namespace crash_reporter {
 namespace internal {
 
-using TransitionalCrashKeyStorage = google_breakpad::
-    NonAllocatingMap<40, kCrashKeyStorageValueSize, kCrashKeyStorageNumEntries>;
+using TransitionalCrashKeyStorage =
+    google_breakpad::NonAllocatingMap<kCrashKeyStorageKeySize,
+                                      kCrashKeyStorageValueSize,
+                                      kCrashKeyStorageNumEntries>;
 
 // Accesses the underlying storage for crash keys for non-Crashpad clients.
 CRASH_KEY_EXPORT TransitionalCrashKeyStorage* GetCrashKeyStorage();