Factor compilation of ~MockProcTable in mock_webgpu.cpp

GMock generates a lot of code in the destuctor of mock classes, so
factor that in mock_webgpu.cpp instead of compiling the code once for
each file including mock_webgpu.h.

Bug: None
Change-Id: I2b5984e911020eb33457bde9c6a45beaa93b3071
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/19725
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>

generator/templates/mock_webgpu.cpp

@@ -149,8 +149,9 @@ void ProcTableAsClass::CallFenceOnCompletionCallback(WGPUFence fence,
     }
 {% endfor %}
 
-MockProcTable::MockProcTable() {
-}
+MockProcTable::MockProcTable() = default;
+
+MockProcTable::~MockProcTable() = default;
 
 void MockProcTable::IgnoreAllReleaseCalls() {
     {% for type in by_category["object"] %}

generator/templates/mock_webgpu.h

@@ -116,6 +116,7 @@ class ProcTableAsClass {
 class MockProcTable : public ProcTableAsClass {
     public:
         MockProcTable();
+        ~MockProcTable() override;
 
         void IgnoreAllReleaseCalls();