Add an explanatory comment

I was hitting an unexpected bug where one of the GWP-ASan tests was
failing on OS X but not Windows. I realized this was because the test
never ran on Windows in the component build (due to how the allocator
shim works on Windows) but was failing when I ported it to OS X. Save
a note to save future devs some debugging time.

Change-Id: I107113eab8e808d8837f5e56b15ca53006436c95
Reviewed-on: https://chromium-review.googlesource.com/c/1379182Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618641}

components/crash/core/common/crash_key.h

@@ -217,6 +217,8 @@ CRASH_KEY_EXPORT void InitializeCrashKeys();
 #if defined(UNIT_TEST) || defined(CRASH_CORE_COMMON_IMPLEMENTATION)
 // Returns a value for the crash key named |key_name|. For Crashpad-based
 // clients, this returns the first instance found of the name.
+// Note: In a component build, this will only retrieve crash keys for the
+// current component.
 CRASH_KEY_EXPORT std::string GetCrashKeyValue(const std::string& key_name);
 
 // Resets crash key state and, depending on the platform, de-initializes

components/crash/core/common/crash_key_crashpad.cc

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // NOTE: This file is only compiled when Crashpad is used as the crash
-// reproter.
+// reporter.
 
 #include "components/crash/core/common/crash_key.h"