Reland "[battery] Add ResourceCoalitionMacTest.Busy."

This is a reland of 856342886a

The waterfall reveals that `cpu_instructions` and `cpu_cycles` are
not populated prior to macOS 10.15. This CL updates expectations
accordingly.

Original change's description:
> [battery] Add ResourceCoalitionMacTest.Busy.
>
> This test verifies that CPU instructions, CPU cycles and CPU time
> reported by `GetCoalitionResourceUsage` increase after burning CPU.
> This is a basic expectations for `GetCoalitionResourceUsage` so it
> should be tested from //components/power_metrics/. In an upcoming
> CL, this will allow removing
> //chrome/browser/performance_monitor/resource_coalition_mac_unittest.mm
> without losing tests.
>
> Bug: 1293465
> Change-Id: I7232bd6b67406600b9fc89b7f7f80ad8db47c5f1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3437567
> Reviewed-by: Patrick Monette <pmonette@chromium.org>
> Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#967015}

Bug: 1293465
Change-Id: I5c7f1c9e3b95223e582a1d71fac093ea95bd9c03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3440717
Reviewed-by: Patrick Monette <pmonette@chromium.org>
Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#967792}

components/power_metrics/resource_coalition_internal_types_mac.h

@@ -60,6 +60,7 @@ struct coalition_resource_usage {
   uint64_t cpu_ptime;
   uint64_t cpu_time_eqos_len; /* Stores the number of thread QoS types */
   uint64_t cpu_time_eqos[COALITION_NUM_THREAD_QOS_TYPES];
+  // `cpu_instructions` and `cpu_cycles` are only populated on macOS 10.15+
   uint64_t cpu_instructions;
   uint64_t cpu_cycles;
   uint64_t fs_metadata_writes;

components/power_metrics/resource_coalition_mac_unittest.mm

@@ -4,6 +4,7 @@
 
 #include "components/power_metrics/resource_coalition_mac.h"
 
+#include "base/rand_util.h"
 #include "components/power_metrics/energy_impact_mac.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/abseil-cpp/absl/types/optional.h"
@@ -69,8 +70,46 @@ coalition_resource_usage GetTestCoalitionResourceUsage(uint32_t increment) {
   return ret;
 }
 
+void BurnCPU() {
+  base::TimeTicks begin = base::TimeTicks::Now();
+  constexpr base::TimeDelta busy_time = base::Seconds(1);
+  [[maybe_unused]] volatile double number = 1;
+  while (base::TimeTicks::Now() < (begin + busy_time)) {
+    for (int i = 0; i < 10000; ++i)
+      number *= base::RandDouble();
+  }
+}
+
 }  // namespace
 
+TEST(ResourceCoalitionMacTest, Busy) {
+  absl::optional<uint64_t> coalition_id =
+      GetProcessCoalitionId(base::GetCurrentProcId());
+  ASSERT_TRUE(coalition_id.has_value());
+
+  std::unique_ptr<coalition_resource_usage> begin =
+      GetCoalitionResourceUsage(coalition_id.value());
+  BurnCPU();
+  std::unique_ptr<coalition_resource_usage> end =
+      GetCoalitionResourceUsage(coalition_id.value());
+
+  ASSERT_TRUE(begin);
+  ASSERT_TRUE(end);
+
+  // Waterfall suggests that `cpu_instructions` and `cpu_cycles` are not
+  // populated prior to macOS 10.15.
+  if (@available(macOS 10.15, *)) {
+    EXPECT_GT(end->cpu_instructions, begin->cpu_instructions);
+    EXPECT_GT(end->cpu_cycles, begin->cpu_cycles);
+  } else {
+    EXPECT_EQ(0u, begin->cpu_instructions);
+    EXPECT_EQ(0u, begin->cpu_cycles);
+    EXPECT_EQ(0u, end->cpu_instructions);
+    EXPECT_EQ(0u, end->cpu_cycles);
+  }
+  EXPECT_GT(end->cpu_time, begin->cpu_time);
+}
+
 TEST(ResourceCoalitionMacTest, Difference) {
   coalition_resource_usage left =
       GetTestCoalitionResourceUsage(/* increment= */ 1);