Bug 1628073 - Make the defaults for the profiler settings nicer for mochitests; r=gerald

The defaults should serve our users. I did some profiling with mochitests
and the defaults weren't ideal. It would be nice if the profiler "just worked"
for most of the situations. It would be great to teach the environment variables
about presets, but for now this will make the profiler easier to use for our
users in the general case.

This patch adds both screenshots and updates the entries count. This causes
additional overhead, but people on low-end devices can still tweak the settings
to remove that overhead.

Differential Revision: https://phabricator.services.mozilla.com/D70091

tools/profiler/core/platform.cpp

@@ -243,7 +243,8 @@ static uint32_t AvailableFeatures() {
 // Default features common to all contexts (even if not available).
 static uint32_t DefaultFeatures() {
   return ProfilerFeature::Java | ProfilerFeature::JS | ProfilerFeature::Leaf |
-         ProfilerFeature::StackWalk | ProfilerFeature::Threads;
+         ProfilerFeature::StackWalk | ProfilerFeature::Threads |
+         ProfilerFeature::Screenshots;
 }
 
 // Extra default features when MOZ_PROFILER_STARTUP is set (even if not

tools/profiler/public/GeckoProfiler.h

@@ -293,7 +293,7 @@ static constexpr mozilla::PowerOfTwo32 PROFILER_DEFAULT_ENTRIES =
 // systems.
 static constexpr mozilla::PowerOfTwo32 PROFILER_DEFAULT_STARTUP_ENTRIES =
 #  if !defined(ARCH_ARMV6)
-    mozilla::MakePowerOfTwo32<1u << 22>();  // 4'194'304 entries = 32MB
+    mozilla::MakePowerOfTwo32<1u << 23>();  // 8'388'608 entries = 64MB
 #  else
     mozilla::MakePowerOfTwo32<1u << 17>();  // 131'072 entries = 1MB
 #  endif