Make CrashKeyBreakpadTest tests more robust

Modified CrashKeyBreakpadTest tests to possibly run in a non-clean
state with some chunks already present. The change is prompted by
CL https://chromium-review.googlesource.com/c/v8/v8/+/1658505 that
adds crashkeys to V8's isolate so, depending on the test execution
order, asserts might fire about having unexpected count of chunks.

Bug: v8:9323
Change-Id: Id89335fcab04ab0eb37bd13ba2a11ecb964e66c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1661082Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Irina Yatsenko <irinayat@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#670163}

components/crash/core/common/crash_key_breakpad_unittest.cc

@@ -12,6 +12,7 @@ namespace crash_reporter {
 class CrashKeyBreakpadTest : public testing::Test {
  public:
   void SetUp() override {
+    internal::ResetCrashKeyStorageForTesting();
     InitializeCrashKeys();
     ASSERT_TRUE(internal::GetCrashKeyStorage());
   }