[Tracing] Remove fields from AllocationContext

These fields will return later on in the form of a trait set as proposed
in the Task Traits proposal. The |AllocationContextTracker| will not
keep track of general-purpose fields.

BUG=524631

Review URL: https://codereview.chromium.org/1427953002

Cr-Commit-Position: refs/heads/master@{#357095}

base/trace_event/memory_profiler_allocation_context.cc

@@ -153,19 +153,6 @@ void AllocationContextTracker::PopPseudoStackFrame(StackFrame frame) {
   tracker->pseudo_stack_.pop(frame);
 }
 
-// static
-void AllocationContextTracker::SetContextField(const char* key,
-                                               const char* value) {
-  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
-  tracker->context_[key] = value;
-}
-
-// static
-void AllocationContextTracker::UnsetContextField(const char* key) {
-  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
-  tracker->context_.erase(key);
-}
-
 // Returns a pointer past the end of the fixed-size array |array| of |T| of
 // length |N|, identical to C++11 |std::end|.
 template <typename T, int N>
@@ -194,22 +181,6 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
     std::fill(dst, dst_end, nullptr);
   }
 
-  // Fill the context fields.
-  {
-    auto src = tracker->context_.begin();
-    auto dst = ctx.fields;
-    auto src_end = tracker->context_.end();
-    auto dst_end = End(ctx.fields);
-
-    // Copy as much (key, value) pairs as possible.
-    for (; src != src_end && dst != dst_end; src++, dst++)
-      *dst = *src;
-
-    // If there is room for more, fill the remaining slots with nullptr keys.
-    for (; dst != dst_end; dst++)
-      dst->first = nullptr;
-  }
-
   return ctx;
 }
 

base/trace_event/memory_profiler_allocation_context.h

@@ -5,12 +5,12 @@
 #ifndef BASE_TRACE_EVENT_MEMORY_PROFILER_ALLOCATION_CONTEXT_H_
 #define BASE_TRACE_EVENT_MEMORY_PROFILER_ALLOCATION_CONTEXT_H_
 
+#include <map>
 #include <string>
 #include <vector>
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
-#include "base/containers/small_map.h"
 #include "base/trace_event/trace_event_impl.h"
 
 namespace base {
@@ -141,18 +141,13 @@ class BASE_EXPORT StackFrameDeduplicator : public ConvertableToTraceFormat {
 // must have static lifetime.
 struct BASE_EXPORT AllocationContext {
   Backtrace backtrace;
-
-  // There is room for two arbitrary context fields, which can be set by the
-  // |TRACE_ALLOCATION_CONTEXT| macro. A nullptr key indicates that the field is
-  // unused.
-  std::pair<const char*, const char*> fields[2];
 };
 
 // The allocation context tracker keeps track of thread-local context for heap
-// profiling. It includes a pseudo stack of trace events, and it might contain
-// arbitrary (key, value) context. On every allocation the tracker provides a
-// snapshot of its context in the form of an |AllocationContext| that is to be
-// stored together with the allocation details.
+// profiling. It includes a pseudo stack of trace events. On every allocation
+// the tracker provides a snapshot of its context in the form of an
+// |AllocationContext| that is to be stored together with the allocation
+// details.
 class BASE_EXPORT AllocationContextTracker {
  public:
   // Globally enables capturing allocation context.
@@ -181,13 +176,6 @@ class BASE_EXPORT AllocationContextTracker {
   // Pops a frame from the thread-local pseudo stack.
   static void PopPseudoStackFrame(StackFrame frame);
 
-  // Sets a thread-local (key, value) pair.
-  static void SetContextField(const char* key, const char* value);
-
-  // Removes the (key, value) pair with the specified key from the thread-local
-  // context.
-  static void UnsetContextField(const char* key);
-
   // Returns a snapshot of the current thread-local context.
   static AllocationContext GetContextSnapshot();
 
@@ -203,9 +191,6 @@ class BASE_EXPORT AllocationContextTracker {
   // The pseudo stack where frames are |TRACE_EVENT| names.
   AllocationStack pseudo_stack_;
 
-  // A dictionary of arbitrary context.
-  SmallMap<std::map<const char*, const char*>> context_;
-
   DISALLOW_COPY_AND_ASSIGN(AllocationContextTracker);
 };
 

base/trace_event/memory_profiler_allocation_register_unittest.cc

@@ -50,7 +50,7 @@ size_t SumAllSizes(const AllocationRegister& reg) {
 
 TEST_F(AllocationRegisterTest, InsertRemove) {
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
 
   EXPECT_EQ(0u, OrAllAddresses(reg));
 
@@ -81,7 +81,7 @@ TEST_F(AllocationRegisterTest, InsertRemove) {
 
 TEST_F(AllocationRegisterTest, DoubleFreeIsAllowed) {
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
 
   reg.Insert(reinterpret_cast<void*>(1), 0, ctx);
   reg.Insert(reinterpret_cast<void*>(2), 0, ctx);
@@ -96,7 +96,7 @@ TEST_F(AllocationRegisterTest, DoubleInsertOverwrites) {
   // TODO(ruuda): Although double insert happens in practice, it should not.
   // Find out the cause and ban double insert if possible.
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
   StackFrame frame1 = "Foo";
   StackFrame frame2 = "Bar";
 
@@ -124,7 +124,7 @@ TEST_F(AllocationRegisterTest, DoubleInsertOverwrites) {
 TEST_F(AllocationRegisterTest, InsertRemoveCollisions) {
   size_t expected_sum = 0;
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
 
   // By inserting 100 more entries than the number of buckets, there will be at
   // least 100 collisions.
@@ -161,7 +161,7 @@ TEST_F(AllocationRegisterTest, InsertRemoveCollisions) {
 TEST_F(AllocationRegisterTest, InsertRemoveRandomOrder) {
   size_t expected_sum = 0;
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
 
   uintptr_t generator = 3;
   uintptr_t prime = 1013;
@@ -203,7 +203,7 @@ TEST_F(AllocationRegisterTest, InsertRemoveRandomOrder) {
 #if GTEST_HAS_DEATH_TEST
 TEST_F(AllocationRegisterTest, OverflowDeathTest) {
   AllocationRegister reg;
-  AllocationContext ctx;
+  AllocationContext ctx = {};
   uintptr_t i;
 
   // Fill up all of the memory allocated for the register. |kNumCells| minus 1