metrics/perf: Fix crash for CPU identities outside CpuUarch table

When running on a system with a CPU family/model beyond the last entry
in the CpuUarch table, the CPU id to CpuUarch mapping code tries to
access an invalid iterator/entry and crashes. Check for this case and
return an empty CpuUarch instead.

Bug: 1021000
Change-Id: I2bc19427a03c0fe6906838bdcb2134021fc213df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1893200Reviewed-by: Gabriel Marin <gmx@chromium.org>
Commit-Queue: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Cr-Commit-Position: refs/heads/master@{#712942}

chrome/browser/metrics/perf/cpu_identity.cc

@@ -91,7 +91,8 @@ std::string GetCpuUarch(const CPUIdentity& cpuid) {
   auto* bound = std::lower_bound(internal::kCpuUarchTable,
                                  internal::kCpuUarchTableEnd, search_elem,
                                  internal::CpuUarchTableCmp);
-  if (bound->family_model != family_model)
+  if (bound == internal::kCpuUarchTableEnd ||
+      bound->family_model != family_model)
     return std::string();  // Unknown uarch
   return bound->uarch;
 }

chrome/browser/metrics/perf/cpu_identity_unittest.cc

@@ -79,6 +79,16 @@ TEST(CpuIdentityTest, DefaultCommandsBasedOnArch_Unknown) {
   EXPECT_EQ("", GetCpuUarch(cpuid));
 }
 
+TEST(CpuIdentityTest, DefaultCommandsBasedOnArch_UnknownUpperBound) {
+  CPUIdentity cpuid;
+  cpuid.arch = "x86_64";
+  cpuid.vendor = "GenuineIntel";
+  cpuid.family = 0xff;
+  cpuid.model = 0xff;
+  cpuid.model_name = "";
+  EXPECT_EQ("", GetCpuUarch(cpuid));
+}
+
 TEST(CpuIdentityTest, SimplifyCPUModelName) {
   EXPECT_EQ("", SimplifyCPUModelName(""));
   EXPECT_EQ("intel-celeron-2955u-@-1.40ghz",