better output from engine layer unit test failures

[flar]

The engine has ostream conversions for most Skia objects, but none of the test files include the files where they are defined. Adding the include file to the layer_test.h file will include them on any file which does unit testing on the engine layers.

[flutter-dashboard]

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[flar]

This PR has no tests because it only affects the console output while running unit tests with failures.

[matanlurey]

Wait just adding this #include changes the test output?

[flar]

Wait just adding this #include changes the test output?

Yes, it includes a bunch of ostream operators that teach the gtest macros how to print out the Skia objects. Without them gtest just defaults to a hex dump of the memory.

[jason-simmons]

GoogleTest is using template lookup to find the best available print function for a given data type (see PrintWithFallback in https://github.com/google/googletest/blob/main/googletest/include/gtest/gtest-printers.h)

Skia does not provide implementations of operator<< or any of the other options for a GoogleTest print function. The engine tree has its own operator<< implementations for Skia types in https://github.com/flutter/engine/blob/main/testing/assertions_skia.h

So there is a risk that the availability of operator<< for Skia types may be inconsistent across TUs, causing GoogleTest's templates to get different results when the lookup is instantiated. The linker may select an instance where the default hex dump print function is the best available, and if that happens the Skia types in the output will not be printed with operator<<.

assertions_skia.h should always be included before gtest.h to ensure that this does not happen.

[jason-simmons]

To ensure that this is always done consistently I'd suggest:

• creating a header that includes assertions_skia.h followed by gtest/gtest.h
• replacing all uses of #include "gtest/gtest.h" in these tests with that header.

[flar]

To ensure that this is always done consistently I'd suggest:

• creating a header that includes assertions_skia.h followed by gtest/gtest.h
• replacing all uses of #include "gtest/gtest.h" in these tests with that header.

I don't think this is worth it. We are on a path to remove Skia geometry objects from most of the engine so we don't need a long term solution. This simple change works fine with minimal changes. I'd like to keep it that simple.

[matanlurey]

test-exempt: header only change for bizarre gtest semantics.